Aircraft Fuel System Icing Inhibitor (FSII)

Fuel System Icing Inhibitor (FSII) is a manufactured fluid which, when added to aviation fuels, helps to prevent the formation of ice crystals in filters, fuel lines and other fuel system components. In many localities, FSII is referred to by the registered, generic trademark "Prist", in others as "D ice". Over the years formulations have changed little. The current commercial fuel is called Jet A.

Icing inhibitor may be added on the flight line or refinery. In both military aviation and civil aviation, the addition of a fuel system icing inhibitor (FSII) to jet fuel is mandatory, depending on flight route, altitude, season and aircraft.

**Note

Fuel system icing inhibitors are added to jet fuel to prevent freezing of the water content at flight altitude. Their concentration in water and therefore the freezing point correlates with the refractive index.

Basic theory on 2 Spool Engines and 3 Spool Engines

For large commercial aircraft engines fuel efficiency will always be a primary concern. History has shown that the long term trend is for fuel costs to increase. More fuel efficient engines reduce the economic impact of fuel price fluctuations on the operator. Another thing to consider are the much tighter emissions regulations being implemented for CO2, NOx, etc.

Improving commercial aircraft turbine engine efficiency can be achieved with higher bypass ratios, higher cycle pressure ratios, higher cycle temperatures, lower mechanical & thermal losses, and improved controls. The higher cost from using more complex engine systems to get better efficiency is almost always a good bargain for large commercial aircraft engines.

A two-spool engine has two concentric shafts that rotate at different speeds: one connects the high pressure turbine stages to the high pressure compressor, and the other connects the low pressure turbine stages to the low pressure compressor and fan. The reason for doing this is that the low pressure stages are larger in diameter, so they have higher tip speed for a given rotational speed. At the same time, the temperature is lower, and so too is the speed of sound. So to keep the flow subsonic, they are designed to rotate at lower speed.

A three-spool engine is the same thing, only with three concentric shafts, the third of which connects an intermediate pressure turbine and compressor.

A geared turbofan uses a transmission to reduce the speed of the fan compared to the low-pressure compressor and turbine, instead of a third spool. This is sometimes used in very high bypass ratio engines, in which the fan is much larger in diameter than the low pressure compressor.

**Advantages of a 3 spool engine:

• More flexible due to aerodynamic matching at part load

• Lower inertia of rotating components

• Easier to start as only one spool needs to be turned by the starter

• Allows for higher ratios of fan air flow to engine flow. This allows for increased thrust without a corresponding increase in jet velocity and reduction in propulsive efficiency leading to high SFC.

**Turbines run closer to optimum speeds

- More efficient

- Easier to start

Note: The older turbo jet engine accelerates a small mass of air to a very high velocity to achieve a given amount of thrust. To obtain the same amount of thrust from a turbofan, it takes a much larger mass of air and does not need to accelerate it to as high of a velocity, thus giving a lower SFC.

**Advantages of double spool engines are:

- Lighter

- Simpler design

- Lower manufacturing cost

What is autopilot? How does it work?

Auto pilot flying aircraft by its own thru computer system.

Flight path stored In flight management and guidance computer. Any modifications required by NOTAMS notices carried out pilot thru MCDU.

Auto pilot command execute by ELAC elevator and aileron computer and FAC flight augmentation computer with AUTO THRUST. So auto pilot controls speed,attitude, altitude hold only and flight envelope protection. Auto thrust controls auto engine thrust in combination with auto pilot. Now pilot need to monitor and communicate with towers on regular intervals.Essentially, autopilot is a very smart and powerful computer that works similarly to a GPS. It can assist the pilot in flying the plane from departure to the touchdown at its final destination.

The autopilot is more accurately described as the automatic flight control system (AFCS). An AFCS is part of an aircraft's avionics -- the electronic systems, equipment and devices used to control key systems of the plane and its flight. In addition to flight control systems, avionics include electronics for communications, navigation, collision avoidance and weather. The original use of an AFCS was to provide pilot relief during tedious stages of flight, such as high-altitude cruising. Advanced autopilots can do much more, carrying out even highly precise maneuvers, such as landing an aircraft in conditions of zero visibility.

The first are the elevators, which are devices on the tail of a plane that control pitch (the swaying of an aircraft around a horizontal axis perpendicular to the direction of motion). The rudder is also located on the tail of a plane. When the rudder is tilted to starboard (right), the aircraft yaws -- twists on a vertical axis -- in that direction. When the rudder is tilted to port (left), the craft yaws in the opposite direction. Finally, ailerons on the rear edge of each wing roll the plane from side to side.

Autopilots can control any or all of these surfaces. A single-axis autopilot manages just one set of controls, usually the ailerons. This simple type of autopilot is known as a "wing leveler" because, by controlling roll, it keeps the aircraft wings on an even keel. A two-axis autopilot manages elevators and ailerons. Finally, a three-axis autopilot manages all three basic control systems: ailerons, elevators and rudder.

**Heading Hold

This will set the desired direction or heading that the pilot wants the plane to take. However, this doesn’t take into account changes due to wind or the desired route; the pilot has to correct that himself.

**Heading and Navigation

This setting will hold a direction as well as navigation. It’s similar to an automated car in that it follows the navigator’s input. The pilot continues to monitor as the plane flies.

**Altitude Hold

In addition to everything above, this feature allows the pilot to set a desired altitude that the aircraft will fly. Some planes have a fancier altitude hold that lets the pilot set a desired climb or descend rate that will make the aircraft automatically climb or descend and then hold that altitude.

**Instrument Approaches

This type of autopilot will fly preprogrammed instrument approaches. The only time the pilot has to take over is to execute the landing.

Why do Airbus aircraft have two auto pilot buttons?

They are controls for two separate autopilot systems that have the same functions, and serve as a backup and crosscheck for each other.

The vast majority of aircraft used by airlines have multiple autopilot systems. These autopilots are essentially the same, they act as backups in case one of the systems fails. The number of autopilot systems depends on the complexity of the aircraft. A Dash 8 has two... A B-767 has three.

Normally one autopilot at a time handles the flying of the airplane. An exception to this rule typically occurs in approach mode, when two (in the Dash anyway) autopilot systems at a time are tied into the flight guidance computer to allow for immediate redundancy should one autopilot fail so near to the ground.

**NOTE

Notwithstanding FAR 135.93(d), autopilot minimum-use altitudes do not apply to autopilot operations when an approved automatic landing system mode is being used for landing. Automatic landing systems must be authorized in an operations specification issued to the operator.

What is Aircraft Pressurization System?

A system which ensures the comfort and safety of crew and passengers by controlling the cabin pressure and the exchange of air from the inside of the aircraft to the outside.

Aircraft engines become more efficient with increase in altitude, burning less fuel for a given airspeed. In addition, by flying above weather and associated turbulence, the flight is smoother and the aircraft less fatigued. Crews will therefore normally fly as close to the aircraft’s Cruise Ceiling as they can depending on flight rules and any other constraints such as the aircraft oxygen system. In order to be able to fly at high attitudes, the aircraft needs to be pressurised so that the crew and passengers can breathe without the need for supplemental oxygen.

The cabin and cargo holds (or baggage compartments) on most aircraft are contained within a sealed unit which is capable of containing air under pressure higher than the Ambient Pressure outside of the aircraft. Bleed Air from the turbine engines is used to pressurise the cabin and air is released from the cabin by an Outflow Valve. By using a cabin pressure regulator, to manage the flow of air through the outflow valve, the pressure within the aircraft can be increased or decreased as required, either to maintain a set Differential Pressure or a set Cabin Altitude.

In practice, as an aircraft climbs, for the comfort of the passengers, the pressurization system will gradually increase the cabin altitude and the differential pressure at the same time. If the aircraft continues to climb once the maximum differential pressure is reached, the differential pressure will be maintained while the cabin altitude climbs. The maximum cruise altitude will be limited by the need to keep the cabin altitude at or below 8,000 ft.

When an aircraft is flown at high altitude, it burns less fuel for a given airspeed than it does for the same speed at a lower altitude. This is due to decreased drag that results from the reduction in air density. Bad weather and turbulence can also be avoided by flying in the relatively smooth air above storms and convective activity that occur in the lower troposphere. To take advantage of these efficiencies, aircraft are equipped with environmental systems to overcome extreme temperature and pressure levels. While supplemental oxygen and a means of staying warm suffice, aircraft pressurization and air conditioning systems have been developed to make high altitude flight more comfortable.

**A safety valve:

acts as a relief valve, releasing air from the cabin to prevent the cabin pressure from exceeding the maximum differential pressure,

acts a vacuum relief valve, allowing air into the cabin when the ambient pressure exceeds the cabin pressure, and acts as a dump valve, allowing the crew to dump cabin air manually.

A Cabin Altimeter, Differential Pressure Gauge, and Cabin Rate of Climb gauge help the crew to monitor the aircraft pressurization.

**Pressurization Terms

The following terms should be understood for the discussion of pressurization and cabin environmental systems that follows:

Cabin altitude—given the air pressure inside the cabin, the altitude on a standard day that has the same pressure as that in the cabin. Rather than saying the pressure inside the cabin is 10.92 psi, it can be said that the cabin altitude is 8,000 feet (MSL).

Cabin differential pressure—the difference between the air pressure inside the cabin and the air pressure outside the cabin. Cabin pressure (psi) – ambient pressure (psi) = cabin differential pressure (psid or Δ psi).

Cabin rate of climb—the rate of change of air pressure inside the cabin, expressed in feet per minute (fpm) of cabin altitude change.

System Operation

The cabin pressurization subsystem is governed by the pressure regulator control, which provides five modes of operation: unpressurized, isobaric, differential cabin-to-ambient pressure, dump, and re-pressurization. Below 5,000 feet, the cabin is normally un-pressurized. Between 5,000 and 25,000 feet, the cabin altitude will remain at 5,000 feet. Maximum cabin pressure-to- ambient differential is 6.7 ± 0.1 psi. 

During the unpressurized mode of operation, the pressure regulator control directs low-pressure air to the pressure regulator valve to command it to the full open position. This mode of operation occurs at all altitudes below 4,350 feet. In this mode, cabin pressure is maintained at a near ambient pressure. The pressure is slightly above ambient because of the duct pressure losses, the quantity of air flowing into the cabin, and the pressure across the internal avionics ventilation subsystem. During flight operations between 5,000 and 24,000 feet, the isobaric mode maintains the cabin altitude between 4,350 and 5,000 feet. The pressure regulator control, using the sensed ambient pressure as a low-pressure source and the sensed cabin pressure as the high-pressure source, modulates the pressure regulator open or closed to maintain cabin pressure at the specific altitude. The differential mode of operation overrides the isobaric mode of operation when the aircraft is flying at altitudes in excess of 24,000 feet. As cabin-to-ambient differential pressure reaches 6.7 ± 0.1 psi, a spring-loaded diaphragm in the pressure regulator control positions a poppet valve to supply this differential pressure as a control pressure to the pressure regulator valve.The cabin pressurization system also makes provision for dumping cabin pressure in an emergency. By setting the cabin pressure switch on the environmental control panel to the DUMP position, the latching solenoids on both the cabin outflow pressure regulating valve and on the cabin safety valve are actuated to the dump position. In addition, the recirculation air shutoff valve will be actuated to the full open position, provided electrical power is available. A secondary method of achieving cabin depressurization is to turn the air-conditioning switch to the OFF/ RESET position and select the auxiliary vent mode. This selection will cause the cabin outflow pressure regulator valve to open, but it will not actuate the cabin safety valve to the open position. The repressurization mode of operation is used when returning to the normal mode from the dump mode or during a rapid descent in excess of 4,000 feet per minute. In this mode, the pressure regulator control modulates the rate of cabin repressurization with an integral isobaric and differential pressure control system. The pressure regulator control compares the existing cabin pressure to a lagging cabin pressure reference. If the result of this comparison exceeds the calibrated rate, control pressure output from the pressure regulator control is reduced. This causes the pressure regulator valve to sense a relatively higher pressure on the opening side of its actuating diaphragm, thus allowing the diaphragm to open the pressure regulator valve butterfly. This reduces cabin pressure and the rate of repressurization. Precautions for operating the S-3 cabin pres-surization subsystem on the ground, where the elevation is 5,000 feet or higher, are required because the cabin pressurization subsystem does not have provisions for automatic repressuriza-tion. Therefore, the cabin will be pressurized whenever the ground elevation is above 5,000 feet. To ensure adequate cooling of the internal avionics during operations at ground elevations above 5,000 feet, one of the following steps must be used: 1. Keep the cabin pressurized as in flight. 2. Set the cabin pressure switch to DUMP to ensure a full-open pressure regulator valve and a full-open pressure safety valve. 3. If the outside air temperature is below 80° F, turn the auxiliary vent selector to ON and open the cabin entry door.

Prepared By: Air.Net Team 

What is term of MEL/CDL? How does dispatcher go through?

MEL - (Minimum equipment List/Leak)

CDL- (Configuration Deviation List)

Basically, MEL refers to Inoperative Ac Parts (broken air-conditioning), while for CDL refers to such missing things (missing winglet or missing flap track fairing).

MEL (Minimum Equipment List) or CDL (Configuration Deviation List) refers to the situation where an aircraft has certain components on the airplane that are inoperative or missing for CDL The aircraft may still be able to fly with these malfunctions, however, a penalty will need to be applied to the performance of the aircraft. The regular flight plan may not be possible and the flight plan may need to be modified. The MEL/CDL functionality in NFP automatically applies the MEL/CDL restrictions to the flight plan so that you do not need to apply them manually.

The following MEL/CDL penalties are cumulative if multiple are applied:

*Etops Time Reduction

*Additional Fuel

*Fixed Tankerage Fuel

*Max Takeoff Weight

*Max Landing Weight

*Driftdown Weight

This means the penalties are added and applied together instead using the most restrictive one.

Air Conditioning/Presurization pack failure in flight or dispatch under MEL relief with one pack inoperative - maximum cruising altitude may be affected. If so, fuel consumption will be higher due to the lower cruising altitude.

In all cases of abnormal operations, be they dispatch under CDL / MEL relief or as a result of an airborne failure, follow the published guidance as prescribed by the manufacturer. This guidance could include (but is not limited to) dispatch criterial, specific fuel penalties for non-standard configurations, emergency drills and checklists or specific directions as published in AOM, Operations Manual or the MEL.

What is Aircraft Conditioning Unit (ACU)?

Aircraft Air Conditioning Unit is one of the major ground support EQUIPMENT is used for aircraft maintenance requirement which supplies cold air or hot air into an aircraft while parked on the ground to sustain comfortable temperatures for passengers in relation to ambient conditions.

Typically, there are 2 types of air conditioning systems are used for aircraft requirements:

1. Air Cycle air conditioning unit

2. Vapor Cycle air conditioning systems.

Most of the turbine-powered aircraft are using Air Cycle air conditioning unit. The vapor cycle air conditioning system is used for reciprocating aircraft process.

Aircraft Air Conditioning Unit comes with

*Towable Trailer mounted

*Skid mounted

*Self-propelled systems with touchscreen *control panel

Aircraft Detection Lighting System (ADLS) 

On the other hand, the technical advances in blades and masts allow the construction of higher and bigger structures, which offer a greater potential for power generation. But this larger size of wind turbines makes them enter into the airspace increasing the danger for aircrafts flights. That’s why is required higher intensity signaling which produces nocturnal discomfort and complaints from populations near wind fields which demands “dark skies” preservation.

Aware of this situation, several types of solution have been tested trying to minimize the impact of the wind turbine’s nighttime light signals. One of the most promising solution is the implementation of a aircraft radar detection, known by the acronym in English ADLS (Aircraft Detection Lighting System).

Currently, to maintain safe aircraft operation in the vicinity of a wind farm at night and in conditions of reduced visibility, CASA may recommend or require the provision of obstacle lighting on wind turbines with a height of 110 m or more. At night the lighting of wind turbines may reduce the risk of aircrew flying into a wind turbine but also provide a source of light pollution to the surrounding community. To balance safety outcomes associated with obstacle lighting with community concern regarding light pollution, an aircraft detection lighting system (ADLS) could be considered in addition to the traditional obstacle lighting solutions.

ADLS is a radar surveillance system which monitors the airspace over and around the wind farm and only activates the obstruction lights when aircraft are in the vicinity of the wind farm. As a result, pilots are made aware of the wind farm location and the public are not disturbed by light emissions during night hours except when necessary.  

There are ADLS systems that are already certified by the United States FAA (Federal Aviation Administration), DFS (Deutsche Flug Sicherung) de Alemania or TBST (Danish Transport, Construction and Housing Authority)

Other countries are in the process of approval, such as Sweden and Finland, but there is still no common regulation in Europe issued by the highest European air safety agency (EASA).

**Note

 "ADLSs continuously monitor the airspace around an obstruction or group of obstructions for aircraft; and when the detection system detects an aircraft in its airspace, the system sends an electronic signal to the lighting control unit, which turns on the lights. Once the aircraft clears the obstruction area and there is no longer a risk of collision, the detection system turns off the lights, and the system returns to standby mode" (FAA). 

What is  Runway Overrun Prevention System (ROPS)?

ROPS is integrated with the aircraft's flight management and navigation systems, and provides the pilots with a real-time constantly updated picture in the navigation display of where the aircraft will stop on the runway in wet or dry conditions.

If the approach profile varies, so does the stopping point. If it will not be possible to stop on the runway, the system provides the crew with a written and spoken "runway too short" warning.

ROPS is made up of two sub-functions, ROW and ROP. The ROW function generates alerts which incite the flight crew to perform a Go-Around whereas the ROP function generates alerts which incite the flight crew to apply available deceleration means.

**ROW = Runway Overrun Warning

**ROP = Runway Overrun Protection

On the Airbus A350 and A380, the ROPS system is directly integrated with Airbus’ Brake-to-Vacate (BTV) which is an autobrake mode that optimizes the deceleration to achieve the runway exit selected by the pilot. 

9 Freedom of Air - Basic Knowledge on AirLaw

1st Freedom of Air

It was also known as technical freedom. “The right to overfly a country without landing. It grants the privilege to fly over the territory of a treaty country without landing. “ Member states of the International Air Services Transit Agreement are granting this freedom (as well as the Second Freedom) to other member states, subject to the transiting aircraft using designated air routes.

2nd Freedom of Air

It was also a technical freedom. “The right to stop in a country for refueling or maintenance on the way to another, without transferring passengers or cargo.”

3rd Freedom of Air

It was the First Commercial Freedom. “ The right to carry passengers or cargo from one's own country to another.”

4th Freedom of Air

“The right to carry passengers or cargo from another country to one's own.” Third and fourth freedom rights are almost always granted simultaneously in bilateral agreements between countries.

5th Freedom of Air

It is also called a connecting flight. “The right to carry passengers from one's own country to a second country, and from that country to a third country.” An example of this could be Emirates Airlines flights originating in Dubai, then going on to Bangkok, and then from Bangkok to Sydney, where tickets can be sold on any or all sectors. Two sub-categories exist. Beyond Fifth Freedom allows the right to carry passengers from the second country to the third country (example silk road). Intermediate Fifth Freedom allows the right to carry passengers from the third to the second country.

6th Freedom of Air

“The right to carry passengers or cargo from a second country to a third country by stopping in one's own country.” Example: Cathay Pacific Airways, Thai Airways, Malaysia Airlines, Singapore Airlines and other airlines in Asia use sixth-freedom rights extensively to fly passengers between Europe and Australia (example : kangaroo road). 

Likewise, American Airlines connects passengers from Europe and Asia to other countries in the Americas via U.S. ports, and British Airways commonly tickets passengers from America to Asia via London. Iceland air sells tickets between Europe and North America via Iceland, Finnair sells tickets from North America to Asia via Helsinki.

7th Freedom of Air

The right to carry passengers or cargo between two foreign countries without continuing service to one's own country.”) The seventh freedom is rare because it is usually not in the commercial interest of airlines, except in Europe where an EU open sky has seen many carriers, particularly low cost carriers, operate flights between two points, with neither of them being in their home country.

8th Freedom of Air

“The right to carry passengers or cargo between two or more points in one foreign country.” The eighth freedom is also known as cabotage, and is extremely rare outside of Europe. The main real life example of eighth-freedom rights is the European Union, which has granted such rights between all of its member states.

9th Freedom of Air

“The right to carry passengers or cargo within a foreign country without continuing service to or from one's own country.” Sometimes also known as stand alone cabotage. It differs from the aviation definition of true cabotage, in that it does not directly relate to one's own country. The EU agreements mentioned above also fall under this category.

What is the difference between Autothrust and Autothrottle? (Basic  Theory)

Basically, Autothrust are wide range usage for Airbus and Autothrottle are wide range usage for Boeing. As far as Autothrust is concerned it has following detents/stops or in simple language thrust limits.Pilots demand the required thrust through these detents. FADEC or full authority digital engine control computer demands the required thrust from the engines depending upon the thrust lever positions.  In Airbus, Thrust lever is based on the "fixed throttle" concept; there's no motorized movement of throttle levers. Means, In case of Auto thrust active, the thrust lever won't move.

The Autothrottle (A/T) is part of the Automatic Flight System (AFS) comprising the Autopilot Flight Director System (AFDS) and the autothrottle.  The A/T provides automatic thrust control through all phases of flight.  The autothrottle system provides automatic thrust control from the start of take-off through climb, cruise, descent, approach and landing or go-around. In normal operation, the FMC provides the A/T system with N1 limit values. The A/T moves the thrust levers with a separate motor for each lever. The A/T can be engaged only when specific conditions are met and disengages automatically when certain conditions are sensed.  While in Boeing, there is an Auto throttle concept in which, throttle lever will move in case of thrust is automatic.  

Vortex Generators (VG)

A vortex generator (VG) is an aerodynamic device, consisting of a small vane usually attached to a lifting surface (or airfoil, such as an aircraft wing) or a rotor blade of a wind turbine. VGs may also be attached to some part of an aerodynamic vehicle such as an aircraft fuselage or a car. When the airfoil or the body is in motion relative to the air, the VG creates a vortex, which, by removing some part of the slow-moving boundary layer in contact with the airfoil surface, delays local flow separation and aerodynamic stalling, thereby improving the effectiveness of wings and control surfaces, such as flaps, elevators, ailerons, and rudders.  

Vortex Generators are simple aerodynamics devices used mainly to keep the airflow attached over a surface and delay flow separation. These are small, fin or vane-like structures attached perpendicular to the surface over which air is supposed to flow and aligned against the direction of airflow at certain angles.  These devices also find applications in the rotor blades of turbines, and even in cars to improve the aerodynamics by reducing overall drag.

Taking the example of a typical aircraft wing, the cross-sectional shape is in the form of an airfoil. This airfoil shape is what allows the aircraft wing to generate a lift force for flight. Airfoils are effective in generating this force only when the air remains attached to its surface.

The angle of attack, as we can see clearly from the diagram, is the angle between the airfoil chord line and the relative direction of airflow. As the angle of attack is increased, the lift force increases. However, this increase in lift force is only up to a certain angle of attack called the stall angle, after which the lift force will start decreasing as the angle of attack increases.

When air flows over the upper surface of the airfoil, the pressure decreases until it reaches the center of lift - about 25% down the airfoil's chord. Then, pressure starts to increase again, so the air moves from an area of low pressure to higher pressure. This is called an ‘adverse pressure gradient’. As the airflow moves towards high pressure from low pressure, it loses energy. Eventually, when it runs out of energy, the airflow separates from the wing.

At higher angle of attack, the normally laminar air flow tends to detach from the surface of the airfoil near its trailing edge region as it loses energy and form vortices. Control surfaces like ailerons, rudder and elevator are located in the trailing edge region. Hence, as the air flow is detached from the trailing edge region, the control surfaces may become ineffective at higher angle of attack and it might become very difficult to try to recover an aircraft from a possible stall.

The air just near the surface of the airfoil forms a boundary layer, which is a thin layer of air that loses energy due to friction. A laminar boundary layer is more smooth and hence, has less skin friction drag (drag over the airfoil surface due to friction).

The air above the boundary layer isn't affected by skin friction, so it has more energy than the air in the boundary layer. Pulling in some of that free-stream air into the boundary layer could add energy and delay the boundary layer's separation. This is where the vortex generators come into play.

Vortex generators act like tiny wings and create mini wingtip vortices, which spiral through the boundary layer and free-stream airflow. These vortices mix the high-energy free-stream air into the lower energy boundary layer, allowing the airflow in the boundary layer to withstand the adverse pressure gradient longer. This allows for the aircraft to operate effectively even at higher angle of attack and prevent stalling.

Essentially, vortex generators convert the laminar boundary layer over an airfoil into a turbulent boundary layer, which despite having more skin friction drag, offers the benefit of keeping the airflow attached to the airfoil surface and makes it more effective at higher angle of attack.

What is Inertial Navigation System (INS) / Inertial Reference System (IRS)? (Basic Understanding)

A GPS receiver is faster, but is only one small piece in a huge system. The GPS ground segment (control and monitoring stations) and space segment (satellites) are necessary for the GPS receivers (user segment in the jargon) to work. They have multiple possibilities to fail, this critical dependency cannot be afforded by an aviation navigation system, GPS must be backed up, and this is done using inertial (can be INS, IRS, IMU or combined with air data units like ADIRU).

IRS is an integrated inertial reference system using RLGs with no navigation function but outputs to navigation and other systems (FMS, autopilot, wx radar instruments etc.) It provides attitude reference and present position information (along with some misc info like speed, heading etc). The position information is provided to separate flight management systems (FMS) that do the navigational computations with pilot interface.

IRS alignment consists of determining local vertical and initial heading. Both accelerometer and laser gyro inputs are used for alignment. The alignment computations use the basic premise that the only accelerations during alignment are due to the earth's gravity; the only motion during alignment is due to the earth's rotation. Accelerations due to gravity are always perpendicular to the earth's surface and thus define the local vertical. This local vertical is used to erect the attitude data so that it is accurately referenced to vertical. Initially, only a coarse vertical is established. Once vertical is established, the laser gyro sensed earth rate components are used to establish the heading of the airplane. As the alignment continues, both the vertical reference and the heading determinations are fine tuned for maximum accuracy.

*NOTE

IRS uses laser ring gyros, that have no moving parts, and sense the difference in the frequency of the laser beam reflected in the system, which in turn allows the computers to calculate, position, movement, speed etc. The basic difference between INS and GPS is how they obtain the planes current position. 

INS (Inertial Navigation System) is a independent on-board navigation system. It does not need any outside inputs or signals for calculating the present position. Before moving the airplane it has to be aligned to the aircraft parking position. (That's why you might have noticed the gate's coordinates displayed near the parking position). 

Describing the way INS works probably would be to scientific. Basically it measures accelerations and rates and then computes its current position based on these signals. This system also supplies data to the aircraft's attitude indication systems. The drawback of INS is that over a longer period of operation, it gets inaccurate. As a rule of thumb, the error will be about 2 nautical miles per hour of operation. 

The GPS (Global Positioning System) needs signals from outside to calculate the present position. These signals are provided by satellites. This system's position is within a tolerance of about 100-something feet. GPSs' disadvantage is that it still is a military system, without a 100% guarantee of availability. For that reason it is not approved for sole means of navigation. It can and is used as a supplementary system on modern aircraft. For example, the INSs' long term deviation mentioned above is corrected with GPS signals.

Instrument Approach Systems – SDF, LDA, and MLS

Simplified directional facility (SDF) provides a final approach course similar to the ILS localizer. The SDF course may or may not be aligned with the runway and the course may be wider than a standard ILS localizer, resulting in less precision. Usable off-course indications are limited to 35° either side of the course centerline. Instrument indications in the area between 35° and 90° from the course centerline are not controlled and should be disregarded.The SDF must provide signals sufficient to allow satisfactory operation of a typical aircraft installation within a sector which extends from the center of the SDF antenna system to distances of 18 NM covering a sector 10° either side of centerline up to an angle 7° above the horizontal. A three-letter identifier is transmitted in code on the SDF frequency; there is no letter “I” (two dots) transmitted before the station identifier, as there is with the LOC. For example, the identifier for Lebanon, Missouri, SDF is LBO.

Localizer Type Directional Aid (LDA)

The localizer type directional aid (LDA) is of comparable utility and accuracy to a localizer but is not part of a complete ILS. The LDA course width is between 3° and 6° and thus provides a more precise approach course than an SDF installation. Some LDAs are equipped with a GS. The LDA course is not aligned with the runway, but straight-in minimums may be published where the angle between the runway centerline and the LDA course does not exceed 30°. If this angle exceeds 30°, only circling minimums are published. The identifier is three letters preceded by “I” transmitted in code on the LDA frequency. For example, the identifier for Van Nuys, California, LDA is I-BUR.

Microwave Landing System (MLS)

The microwave landing system (MLS) provides precision navigation guidance for exact alignment and descent of aircraft on approach to a runway. It provides azimuth, elevation, and distance. Both lateral and vertical guidance may be displayed on conventional course deviation indicators or incorporated into multipurpose flight deck displays.The system may be divided into five functions, which are approach azimuth, back azimuth, approach elevation, range; and data communications. The standard configuration of MLS ground equipment includes an azimuth station to perform functions as indicated above. In addition to providing azimuth navigation guidance, the station transmits basic data, which consists of information associated directly with the operation of the landing system, as well as advisory data on the performance of the ground equipment.

Strategic Lateral Offset Procedures (SLOP) 

SLOP are approved procedures that allow aircraft to fly on a parallel track to the right of the centre line relative to the direction of flight. An aircraft’s use of these procedures does not affect the application of prescribed separation standards.  SLOP allows pilots to fly either the centreline, 1NM or 2NM to the right of centreline. SLOP may be applied from the Oceanic entry point, returning to centreline at the Oceanic exit point, by any aircraft with automatic offset programming capability".

**Centreline SLOP

Our recommendation is not to fly the airway centreline unless you absolutely have to – which will be because ATC mandates it (ie. no SLOP allowed), or because your aircraft can’t (ie. It’s old).

Although SLOP is generally allowed 0nm, 1nm, or 2nm right of track, the 0nm offset is by definition not an offset. Flying centreline:

• increases the risk of collision with opposite direction traffic, either erroneously at the same level as you, or carrying out an emergency descent and not turning away from the centreline as they should.

• increases the risk of wake turbulence from opposite direction traffic also on the centreline.

*Note

Aircraft flying offset tracks must have automatic offset tracking capability - something which is routinely provided in most modern Flight Management Systems. Flight crew are expected to determine the most suitable track using the best traffic information sources available to them. These may include RTF, Airborne Collision Avoidance System (ACAS), visual acquisition and Automatic Dependent Surveillance Broadcast (ADS-B). Communication with other aircraft in the vicinity using the air-to-air frequency 123.45 MHz may also facilitate useful co-ordination.

Altitude, Attitude and Heading Hold?

These are generally 3 different auto pilot modes. The first two are related to pitch and the third to heading/roll are as per below:

Altitude Hold: Generally speaking setting an autopilot to altitude hold will cause the autopilot to maintain that altitude by varying the pitch of the aircraft. Depending on the system it may attempt to maintain the altitude even its not possible which can lead to a dangerous situation.

Attitude Hold: Is the autopilot setting that will hold the pitch of the aircraft constant when set to this mode. For example if you depart and climb out at an 8 degree nose up attitude, engage attitude hold, the aircraft will hold 8 degrees nose up until set otherwise or shut off. As noted in the comments this can create a very dangerous situation as the aircraft may continue to maintain pitch (generally for a climb) even if power does not allow this can cause a stall at high altitude. More sophisticated auto pilots allow for constant airspeed climbs which are far safer.

Heading Hold: This is a roll control mode that holds the heading of the aircraft (keeps it on track). It will typically be slaved to a bug on the HSI where you can set the heading the autopilot flies.

Altitude means the distance between your aircraft and the Sea Level, or in simple terms, how high you are from the 0 feet. although this might be differ in different pressures, that is why aircraft can adjust its altimeter setting for standard pressure.

Attitude means the orientation of your aircraft relatives to the horizon, including Pitch (relative to Y-Axis), Roll (Relative to X-Axis, and Yaw (Relative to Z-Axis).

Landing Gear Control Interface Unit (LGCIU) Fault

So, what is the function of LGCIU?

Two Landing Gear Control and Interface Units (LGCIUs) control the extension and retraction of the gear and the operation of the doors. They also supply information about the landing gear to ECAM for display, and send signals indicating whether the aircraft is in flight or on the ground to other aircraft systems.There are 2 LGCIU’s fitted on the A320. One LGCIU controls one complete gear cycle, then switches over automatically to the other LGCIU at the completion of the retraction cycle. It also switches over in case of failure.

The FADECs use LGCIU input to determine idle mode. If a LGCIU is determined to be faulty, the system failsafes to approach idle mode, and modulated idle and reverse idle (and hence reversers) will not be available.

The GPWS uses LGCIU 1 to determine landing gear position. If this LGCIU is faulty, the GPWS will need to be inhibited to prevent spurious warnings.

*Note

The landing gear positions are indicated by 2 triangles for each gear on the ECAM WHEEL page. The left triangle is controlled by LGCIU 1, the right one by LGCIU 2. Left or right amber crosses in place of the triangles indicate respectively that LGCIU 1 or LGCIU 2 is failed.

If both LGCIUs are lost, normal landing gear control and indicating systems are lost. The gear must be gravity extended (see Section 8.3, “Gravity extension”). Additionally, the autopilots and autothrust are lost (normal law remains available) and wing anti-ice is limited to 30s of heating (i.e. the ground test), the only indication of which is a “no Anti-Ice” message on the BLEED SD page.

By Air.Net Team 

What is difference between Aircraft Taxing, Take-off and landing Lights?

There are basically two types of (exterior) lights in an aircraft- the navigational lights, which are required to be switched on from sunset until sunrise and other forms of exterior lights, which can be switched off at the pilot or operated only at some parts of the aircraft operation, like the landing/taxi lights.

A (non-exhaustive) list of aircraft lights:

Navigation lights All aircraft are equipped with a steady light near the leading edge of each wingtip. The starboard light is green while that on the port wing is red. The different colors make it possible for an outside observer, such as the pilot of another aircraft, to determine which direction the plane is flying. These are required to be on during operation (in night).

Navigation or Position lights In addition to the red and green lights, most large planes like airliners are also fitted with other steady white navigation lights in various locations like the trailing edges of each wingtip, horizontal tail and top of the vertical tail. The main purpose is to increase the visibility of aircraft from behind.

Anti-Collision Beacon lights These are are flashing (or strobe) light assemblies installed on the upper and lower fuselage of aircraft,used to improve visibility of the aircraft. These can be switched off at the discretion of the pilot under some conditions.

Strobe lights High-intensity strobe lights that flash a white-colored light are located on each wingtip. These flashing lights are very bright and intended to attract attention during flight. They are sometimes also used on the runway and during taxi to make the plane more conspicuous.

Logo lights These steady white lights on the surface of or at the tips of the horizontal stabilizer are used to illuminate the company's logo painted on the vertical tail. These are usually switched off in airports to improve the visibility of the aircraft.

Aircraft Lights

1) Navigation lights 2) Aft light 3) Anti-collision strobe lights 4) Logo light "Jet-liner's lights 1 N" by CC BY 3.0 via Commons.

Wing lights Many airliners feature lights along the root of the wing leading edge that can be used to illuminate the wing and engine pylons in flight. These lights may be used to make the plane more visible during takeoff and landing or to inspect the wings for damage in flight. Pilots can also use the wing lights to inspect the wings and slats for any ice accretion that might build up when flying through clouds.

Taxi lights A bright white lamp is located on the nose landing gear strut of most planes. This light is typically turned on whenever the aircraft is in motion on the ground for greater visibility during taxi, takeoff, and landing.

Landing lights Typically the brightest light in the aircraft, these are fitted on most planes (and helicopters) for enhanced visibility during the landing approach. These lights can also be used to illuminate the runway at poorly lit airports. They can be located in the wing root, in the outboard wing, or somewhere along the forward fuselage (the usual location incase of helicopters), with some aircraft having them in more than one location.

Boeing 787 lights

Runway Turnoff lights Usually located in the leading edge of the wing root, these bright white lamps are intended to provide side and forward lighting during taxi and when turning off the runway. These lights are most useful at poorly lit airports but are usually unnecessary. The lights can also be used in flight if greater visibility is required.

Wheel Well lights Some planes are equipped with additional lights in the nose and main gear wheel wells. These lights are provided primarily to assist ground personnel in making pre-flight inspections of a plane at night.

Landing light is very, very bright. You turn it on when you want to see what's in front of the aircraft, or you want everybody to notice you. On a clear night you can easily spot an aircraft heading towards you with its landing light some 10 miles away. When you enter a runway, you turn on the landing lights as a way to shout "I'm here. Don't collide on me" to everybody. If every pilot turns on the landing light at the gate, some ground crews will sure get blinded sooner or later.

If you're on a runway, turn on everything.

If you're on a taxiway, turn off your landing light but keep your taxi light on. Lights like logo & wing light are optional.

Many aircrafts, especially the smaller ones, do not have wing lights. Some aircraft use the same light as landing & taxi light, in which case you should turn it on during taxi as well unless you want to taxi in the dark.

The difference between taxi and landing lights is similar to low and high beam lights in car. Landing lights are much brighter, which is needed to give sufficient visibility during high-speed take-off and landing roll and to make the plane visible from several miles away when in flight, but they would be blinding when used on the apron, so less powerful taxi lights are used when taxiing.

Ultra-light aircraft may not be equipped with any lights at all, so not all aircraft have them, but all aircraft that may be operated at night do. Small aircraft (like Cessna 172) often have the taxi and landing light installed together under one cover, but in most cases there are still two bulbs with different brightness.

Prepared by: Air.Net Team 

Radar Systems (Basic)

Ground RADAR used by ATC are used to fix an aircrafts position which allows ATC to separate aircraft and guide the pilot.

Three ground RADAR systems used by ATC include:

1. En-Route Surveillance Radar (RSR)

2. Terminal Approach Radar (TAR)

--Primary Surveillance Radar (PSR)

--Secondary Surveillance Radar (SSR)

3. Surface Movement Radar (SMR)

**En-Route Surveillance Radar (RSR)

En-Route Surveillance Radars (RSR) are long range radars which the signal goes to 300 NM. It operates with frequency between 1 to 2 GHZ. It used for airway surveillance to provide range and bearing of aircraft.Surveillance: close observation, especially of a suspected spy or criminal.

**Terminal Approach Radar (TAR)

TAR is a high definition radio detection device which provides information on Identification, Air speed, Direction and Altitude of aircraft. It is use to assist ATC to track the position of aircraft in the air within the vicinity of the airport. Enable him to effect separation of aircraft to a finer degree than possible with information exchange by voice communication between the pilot and the controller.

*Primary Surveillance Radar (PSR)

The advantage PSR is that it operates totally independently of the target aircraft. Means that no action from the aircraft is required for it to provide a radar return. But PSR only provides direction and distance of aircraft. Primary Surveillance Radar (PSR) transmits a high power signal. When a signal strikes an object or target, some signal energy is reflected back and is received by the radar receiver.

RADAR receiver will plot the direction and the distance of the target (aircraft) from the radar station. Thus, the ATC could know the position of aircraft through the RADAR display.

*Secondary Surveillance Radar (SSR)

Secondary Surveillance Radar (SSR) transmits an interrogation signal which is received by the target aircraft. The aircraft transponder sends back a coded reply to the ground radar equipment. From the coded signal, information of the aircraft’s call sign, altitude, speed and destination. SSR requires an aircraft to be fitted with a transmitter or receiver called as transponder.

Advantages:

1) Requires much less transmitting power to provide coverage up to 200 to 250NM.

2) Provides more information: aircraft’s identity (its code & call sign), indicates aircraft’s altitude, speed & destination.

3) Reply signal is much stronger as it does not rely on returning reflected signals.

**Surface Movement Radar (SMR)

SMR installed at the airport (at top of ATC tower building). SMR provides a very accurate radar display in all weathers and conditions of visibility. SMR radar display can show all of the airfield infrastructure including aircraft movements on runway, taxiway and apron. It is designed to provide clear display of all aircraft on runway or taxiway so that ATC can ensure:

a) Runway are clear for take-off/landing

b) Guide aircraft to apron in order.

The surface movement radar (SMR) allows the Air Traffic Controller to 'see' in real time the aircraft and vehicles movements into the airport control area. Surface movement radar can improve both safety and efficiency of airport traffic by providing the ground controller with a clear picture of the areas or under poor visibility conditions.

What is Overdue Aircraft?

Consider an aircraft to be overdue, initiate the procedures stated in this section and issue an ALNOT when neither communications nor radar contact can be established and 30 minutes have passed since:

NOTE- The procedures in this section also apply to an aircraft referred to as “missing” or “unreported.”

What is QALQ (Code asking if Transmit to departure tie-in FSS communications check aircraft has landed or or FSS where flight plan is on file returned to station) The destination station transmits a QALQ message to the departure station after the initial communication check fails to locate the aircraft. Upon receipt of the QALQ inquiry, the departure station shall check locally for any information about the aircraft and take the following action:

• If the aircraft is located, notify the destination station.

• If unable to locate the aircraft, send all additional information to the destination station, including any verbal or written remarks made by the pilot that may be pertinent.

• If the aircraft is located, the destination station shall transmit a cancellation message.

What is ALNOT (Alert Notice)?

ALNOT t is "a request originated by a flight service station (FSS) or an air route traffic control center (ARTCC) for an extensive communication search for overdue, unreported, or missing aircraft," explains the Aeronautical Information Manual. Conduct a communications search of those flight plan area airfields, which fall within ALNOT search areas and were not contacted during an INREQ search. The ALNOT will be issued at the end of the INREQ or when the estimated time that the missing aircraft's fuel would be exhausted or when there is serious concern regarding the safety of the aircraft and its occupant

What is INREQ (Information Request)?

it is done within 30 minutes after the aircraft is overdue which destination airfield allowed to send INREQ. It is send to the departure airfield, FSS, and the Air Route Traffic Control Centers along the route of flight .

What is Engine Hung Start?

The "hung" start happens when an engine is accelerating towards idle RPM, with normal combustion, and an extraction of bleed air occurs. So, the engine never reaches idle RPM but instead keeps running in a lower stage.

Question is, does it respond anyway to throttle movement?

So the answer should be yes, because A hung start happens if the engine stops accelerating towards the idle RPM or "rolls" back after reaching idle. The only correct action in this case is to shutdown the engine! Never advance the throttles in this case. As the airflow through the engine is too low you can easily overshoot the max. EGT (hot start)by introducing more fuel which it depending on the time of the EGT.

**The Start System

Each engine is fitted with an air starter motor, when engine start is selected, each starter motor will be supplied with air from either the APU, The ground start unit or engine which is already running and capable of supplying air.

APU - the aircraft's normal bleed air system ducting is utilized to pass the air to the starter motor. Non return valves prevent leaking back into the engine compressor during engine start..

**The hung start

The EGT being higher than would be expected for the RPM at which the engine has stabilized

The RPM being lower than the engines self sustaining speed

The usual cause of a hung start is insufficient airflow to support efficient combustion and there could a number of reasons for this.

For instance at a high altitude airfield, starting an engine which has a contaminated compressor Or, insufficient motive power being applied to the starter motor will prevent the compressor pushing required amount of air through the engine.

A hot start is when the EGT exceeds the safe limit. Hot starts are caused by too much fuel entering the combustion chamber, or insufficient turbine r.p.m. Any time an engine has a hot start, refer to the AFM, POH, or an appropriate maintenance manual for inspection requirements.

If the engine fails to accelerate to the proper speed after ignition or does not accelerate to idle r.p.m., a hung start has occurred. A hung start, may also be called a false start. A hung start may be caused by an insufficient starting power source or fuel control malfunction.

Engine Start

The process of the engine starting follows this basic formula

**Through the opening of bleed air valves, bleed air is sent to an air turbine starter. These devices typically use the high pressure bleed air to spin and engage a centrifugal clutch connected to the engines accessory drive. This in turn causes the N2 shaft within the engine to spin.

**With the N2 shaft spinning, the N2 compressor and the N2 turbines are spinning. This begins to force air through the engine from front to back.

**With the accessory shaft and N2 shafts spinning, accessories should start working and this can be verified by oil pressure indications on the EICAS.

**With increased N2 rotation, ignition will be turned on. These igniters are located in the hot section of the engine and produce small sparks. There should be an indication on the EICAS that the ignition is active.

**With further increase in N2 rotation, fuel flow will be introduced. This will be verified on the EICAS. Once fuel flow is noted, it is important that the next stop happen fairly soon.

**Light off! The fuel is lit by the ignition and now the fire burning in the hot section supplied by air from the compressor is producing thrust across the N2 and N1 turbines.

**As the engine is producing thrust across on the N1 turbine, the N1 shaft is spinning the N1 fan and the EICAS will note this increase in N1 rotation. N1 and N2 rotation speeds increase.

**Above a N2 threshold, bleed air valves supplying the the air turbine starter will close and the starter disengage. The igniters will turn off at some N2 threshold.

**The engine will settle into a stable idle thrust setting.

What can go wrong?

1)Hung start

-N2 fails to spin up sufficiently for fuel flow to be introduced.

-Each start has a time limit and the start will be aborted.

2)No ignitors

-Abort the start and switch igniters.

-Give MX a call.

3) Failure to ignite

-Fuel flow is introduced but light off has not occurred in a proper timeframe

-Fuel is building up in the engine and if light off does occur, it can be damaging.

-The start is aborted and dry motoring is performed to clear the engine.

4)ITT exceedance

-There is usually a limitation in the inter-turbine temperature during engine start.

-If this is exceeded the start must be aborted

-This may require coordination with MX before another start is attempted.

5)The air turbine starter fails to disengage

-This must be corrected before departing

-In some engines, MX can correct this with the engine running.

6) The bleed air shutoff valve supplying the air turbine starter fails to close

-This may require an engine shutdown to remedy

-However, in some airplanes, this valve can be manually shut by MX with the engine running

-Coordination with MX required.

7) Runaway N1 or N2

- If the FADEC isn't managing fuel flow properly, the engine may not settle but continue to spin up.

- Abort the start.

Coordinate with MX before attempting a restart.

What about starting the engine in the air?

If the engine suffers a flame out, an airborne restart may be attempted. These starts typically happen one of a few ways:

1) Cross-bleed start

2) APU start

3) Windmilling start

The APU start is essentially the same process as above. The crossbleed start, which can also be done on the ground, merely substitutes a running engine at a high power setting to provide the bleed air for starting and is otherwise the same as above.

The interesting start is the windmilling start. The necessity for this means something bad has happened. To need a windmilling start, this means that there are no bleed air sources to supply the air turbine starter. This can mean that all engines are out and the APU is unavailable (BAD!), or merely that bleed valves to a shutdown engine have failed closed and are unable to be opened.

For the EMB-145 that I am familiar with, a windmilling start required descending at an airspeed between 260 KIAS and 320 KIAS and could not be attempted above FL250. In short, you hope that the mass flow through the engine is enough to spin the N2 compressor as the ATS would. With an N2 indication within the engines airstart envelope, you introduce spark and fuel and hope that the engine lights. In the worst case, if you too slow and unable to provide enough airflow prior to light off, the engine can quickly overtemp and be damaged. For this reason it is especially important to abort this kind of start as soon as an abnormality is detected.

What is Ground Power Unit (GPU)?

The Red Box range of ground power units (GPU) are designed to offer every variation of power needed for Aircraft, Vehicles, the rail industry and the military.

We have a full range of portable start units (including lithium GPU’s), continuous DC power supplies, combination start and continuous power units, transformer rectifier units.

This is a ground power unit (GPU) which supplies the aircraft with electricity while the generators or the auxiliary power unit (APU) are not running. This is important especially during boarding, when the cabin lighting needs to remain on for passengers to embark or disembark. The GPU is also used to start the APU, which in turn provides electricity to start the engines and the generators. A ground power unit (GPU) is a vehicle capable of supplying power to aircraft parked on the ground. Ground power units may also be built into the jetway, making it even easier to supply electrical power to aircraft.

Many aircraft require 28 V of direct current and 115 V 400 Hz of alternating current. The electric energy is carried from a generator to a connection on the aircraft via 3 phase 4-wire insulated cable capable of handling 261 amps (90 kVA). These connectors are standard for all aircraft, as defined in ISO 6858.

What Are Flight Segments in Aviation?

The terms associated with air flights might sound very foreign if you are not a seasoned traveler. Flight segment is a term typically applied to portions of an itinerary where you will land in multiple cities along the way. However, technically all flights have at least one flight segment on a nonstop flight, the segment is from the city where you take off to your final destination.

Look for the term "stop" when choosing a flight itinerary. For example, if you see "2 Stops" next to a flight, you will land twice en route to your final destination. According to the International Air Transport Association, or IATA, flight segments refer only to stops where the next flight continues under the same flight number. Every stop adds another flight segment. For instance, if you have two stops under the same flight number, you will have three flight segments: city A to city B, city B to city C and city C to city D.

Pay attention to the amount of time between segments. If you are traveling from Los Angeles to New York with a stop in Chicago, for instance, compare the landing time for the Los Angeles to New York segment with the take-off time for the Chicago to New York segment. If the time between segments is very short, you are more likely to miss your second segment in the event the first flight runs behind. Choose a flight with at least one full hour between segments to give yourself some wiggle room.

Comparison of Flights and Legs

A flight is defined by the IATA as the operation of one or more flight legs with the same flight designator. Unlike a flight segment, a flight may involve one or more aircraft. The IATA defines a leg as the operation of an aircraft from one scheduled departure station to its next scheduled arrival station. A flight segment can include one or more legs operated by a single aircraft with the same flight designator.

Leg vs Segment in layman terms:

A leg stops when the plane lands.

A segment stops either when you change flight number of when you arrive at one city where you want to spend time.

One segment includes one or more legs from the same flight number. Sometimes a plane lands to refuel or to load other passengers but is technically the same flight number. Every ticket's coupon represent a segment.

As defined by others:

A leg is always a single non-stop flight. Example, UA123 from BOS-EWR is a leg.

A segment is a flight operated by a single flight number, but may have an intermediate stop....Example - UA 234 from BOS-ORD-SFO is a segment

"Slice" is a newer and less used term in the travel industry:

A slice can be a single flight segment or multiple flight segments to get from origin to destination, possibly with a connection, but without a stopover.

Example- round trip itinerary with two slices

Slice 1 - UA123/15NOV BOS-EWR Slice 1 - UA234/15NOV EWR-SFO

Slice 2 - UA345/25NOV SFO-BOS

What is trimmed aircraft ?

Trimming is cutting out the control forces to zero. It is used in take off, cruise and landing (yes, all the time). In General aviation aircraft, this is achieved by an elevator and a trim tab combination. When the pilot push the controls, the elevator moves down creating an up force through the hinge and creates elevator hinge moment.

To keep this going with minimal or no inputs from the pilot, he adjusts the trim. In this situation, nose down trim is applied. This moves the trim tab up generating a down force. This force also acts through the elevator hinge. Once the tab moment and elevator moment becomes equal the aircraft will be in trim. That is zero stick force will be required to maintain the flight in the regime.

In Commercial airplanes things are a lot different. Because of their size a small trim tab is not going to be much of an use. But they also need a way to stay nicely trimmed. To achieve this, they have something called a Variable Incidence tailplane. As the name suggests, the pilot can vary the incidence angle of tailplane here. Still, the pilot to control the pitch pulls the elevator up or push it down. Let's look at an example. If the pilot wants to move up, he would move the elevator up. To trim the airplane the pilot now will have to apply nose up trim. As he does this, the tailplane will decrease its incidence via a jack screw. This is continued until the elevator and the tailplane are inline. This balances load from both surfaces which makes the stick forces zero.

How variable incidence tailplane works?

Some advantages of VI tailplane include a more powerful means of trim, can operate at higher ranges of CG and lower drag profile as less of the airplane is exposed to the air flow. One disadvantage is if the trim runs out of position, the airplane might go bonkers. As tailplane creates a much higher moment, there is no way the much smaller elevator can neutralise it. But there are mechanisms placed to avoid this.

One final point. Fly by wire aircraft have auto trim. So, Airbus pilots don't have to trim the airplane. It is done automatically by the computer.

In simple Understanding, The word Trimming is used at two places in an aircraft. One, which is not very common, is 'Fuel trimming'. This is done when pilot wants to reduce fuel flow for a given throttle setting to keep the EGT or TGT in control. But the most widely used application of trimming is in the flying control system.

When an aircraft flies level and steady, it is supposed to fly hands free. But in case there is some minor problem or maladjustment in the control system or disturbance of CG, the aircraft might deviate from its level flight automatically. For example it can fly left or right, it can fly one wing low or it can fly with a nose up or nose down attitude. So to keep it in level flight, the pilot need to hold the concerned control in opposite direction. (As per my example the rudder pedal or the aileron controls or the elevator controls). Don't you think this would be cumbersome for the pilot to hold a control continuously and fly for longer time. So there are trimmers available in every control system which can be operated by the pilot in desired direction and it will move the control to eliminate the error existing in that system rather trim the control and in turn the aircraft.

Trimming is done by moving a small control surface attached to the trailing edge of the main control surface known as trim tab. It can be moved by mechanical linkage or electrically. In many hydraulically operated controls, the complete control surface is moved slightly when trimmed.

Note***Please do not confuse Trim Tabs with Balance Tabs and Spring Balance Tabs. They look similar but their purpose is different.

(APU) What about it all ?

APU stands for auxiliary power unit.

It provides the aircraft electricity and bleed air. In german APU translates to "Hilfstriebwerk". This directly translated into english means "Helping engine". That's why some german speaking people think this is an additional engine to provide thrust for the aircraft. The APU does not produce any thrust when running. However, it can help the engines producing more thrust, when turned on.

The APU generates following power:

• Pneumatic power

• Electrical power

• Hydraulic power (Indirectly)

The main uses for the APU are following:

• Providing electricity at the gate, when no engines are running

• At most airports, big enough to fit an aircraft equipped with an APU, there are GPU's (Ground Power Unit) available. A GPU is the same as an APU, but is on ground, connected with the aircraft.

• GPU connected to aircraft

There is also the Air Start Unit, a ground based system providing pressure air and the Air Conditioning Unit, ground based as well and providing air conditioning.

However, if the airport isn't equipped with such units or there is another reason they can't be used, the APU can replace all of them.

It is providing the electricity for the plane and the bleed air for the packs (air conditioning) and the engine start.

But note: The above mentioned ground units, usually don't replace the APU if they are available. Because usually, the engines are started during pushback, there can't be a ground unit connected to the aircraft.

To answer your question for this part, when the APU goes on and off: It usually will be turned on before pushback, or if there is no GPU, upon entering the cabin. After all engines have started and are stabilized, the APU can be turned off.

• Relieve the engines during take-off by using bleed-air from the APU

If full power is needed for the take-off, what is rare, the engine bleed can be turned off, as bleed air by the engines decreases power. That also means, no air conditioning. If the pilots want air conditioning during take-off, they can turn on the APU and use it's bleed air.

• Providing electricity in-flight in case of engine-failure(s)

In case of an engine failure the APU is turned on, to assure the operation of all aircraft systems. The electrical power for the avionics and the hydraulic power to control the control surfaces.

• Providing bleed-air to start the engines.

All big jet aircraft are using pneumatic power to crank the engines. This can be done with the bleed air of the engine, the Air start unit on the ground or the APU. As mentioned above, engines are usually started during pushback, so the APU is mostly used to achieve this task.

Turning the APU on is also an item on the after landing checklist. As the APU needs some time to spool up as well, it is started after landing. When at the gate, the engines can be shut down directly. The APU just supply electricity for the period between engine stop and connection of the GPU.

Difference between Wave drag and Ram drag

Drag is the aerodynamic force that opposes an aircraft's motion through the air. Drag is a force and is therefore a vector quantity having both a magnitude and a direction. Drag acts in a direction that is opposite to the motion of the aircraft. Lift acts perpendicular to the motion. There are many factors that affect the magnitude of the drag. Many of the factors also affect lift but there are some factors that are unique to aircraft drag.

Two additional sources of drag are wave drag and ram drag. As an aircraft approaches the speed of sound, shock waves are generated along the surface. The shock waves produce a change in static pressure and a loss of total pressure. Wave drag is associated with the formation of the shock waves. The magnitude of the wave drag depends on the Mach number of the flow. Ram drag is produced when free stream air is brought inside the aircraft. Jet engines bring air on board, mix the air with fuel, burn the fuel, then exhausts the combustion products to produce thrust. If we look at the basic thrust equation, there is a mass flow times entrance velocity term that is subtracted from the gross thrust. This "negative thrust" term is the ram drag. Cooling inlets on the aircraft are also sources of ram drag.

What is Holdover Time (HOT)?

Holdover Time (HOT) is the estimated time for which an anti-icing fluid will prevent the formation of frost or ice and the accumulation of snow on the protected surfaces of an aircraft, under specified weather conditions.

Holdover Time is determined by the extent to which it is expected that applied fluid will remain active on the aircraft surfaces; active fluid must be able to provide protection from the accretion of frozen or semi-frozen contaminants in the prevailing conditions. Holdover Time begins at the start of the anti icing operation. If a two-step operation is used, then it begins at the start of the final (anti-icing) step. By definition therefore, holdover time will have effectively run out when frozen deposits start to form or accumulate on treated aircraft surfaces.

Due to their properties, Type I fluids form a thin liquid wetting film, which provides only an extremely limited holdover time, especially in conditions of freezing precipitation. With this type of fluid, no additional holdover time can be obtained by increasing the concentration of the fluid in the fluid/water mix.

For ‘thickened fluids’ of Type 2, 3 and 4, their pseudo-plastic thickening agent enables the fluid to form a thicker liquid wetting film on aircraft surfaces which can then provide a significantly longer holdover time, especially in conditions of continuing freezing precipitation. With this type of fluid, additional holdover time will be provided by increasing the concentration of the fluid in the fluid/water mix, with maximum holdover time available from undiluted fluid.

Full Authority Digital Engine Control (FADEC)

FADEC is a system consisting of a digital computer, called an electronic engine controller (EEC) or engine control unit (ECU), and its related accessories that control all aspects of aircraft engine performance.

The FADEC monitors inputs such as:

*Shaft speeds

*Engine temperatures

*Oil pressures

*Actuator positions

*Power setting and then sets fuel flow, variable stator vanes, and air bleed valves

Using FADEC (possibly also called a DECU) rather than a mechanical unit generally saves a lot of complexity and weight, and results in a more reliable system of engine control. The engine is controlled not just by input of the throttle lever position, but also atmospheric parameters, engine pressure, engine temperature. These are all sampled many times a second, and the FADEC unit controls not just fuel input to the engine, but other variables eg variable guide vane position, use of bleed valves etc.

FADEC is a full authority system, i.e. it controls engine operation and parameters at all speed regimes. It has no backup system.

EEC is a supervisory system which controls engine parameters and operation to prevent parameter exceedance (temperature, RPM, etc.),and comes into operation at certain engine speeds. It has a backup in case all the channels of EEC are lost. The EEC is dual redundant with all subs-systems such as sensors, cables etc duplicated, so that a single fail leaves the system fully operational.

It is housed either in the airframe, or like in civil airliners on the engine, leaving it in need of protection of extreme circumstances:

*Temperature - ice and tropical heat.

*Electromagnetic radiation - lightning and airport radar

*Engine vibration

What is ULD in aviation?

Unit Load Devices (ULD) are used as containers for baggage and cargo carried in the holds of suitably dimensioned and equipped aircraft and are secured so that they cannot move within the hold in flight.

Each Aircraft Unit Load Device (ULD) is identified by its ULD code. This code is a unique combination of letters and numbers, starting with a three-letter prefix that indentifies the type of ULD. This prefix is followed by a unique 4 or 5-digit serial number to distinguish it from others of the same type. The last two or three characters designate the owner of the ULD (e.g. the airline).

Many different parties handle ULDs as they pass between airlines and airports around the world, so a system was needed to identify easily and quickly each ULD. Therefore, the International Air Transport Association (IATA) introduced a global standard system of identification. Accordingly, each ULD is assigned a unique ULD code, which is clearly visible on the relevant unit. By standardising the system, all manufacturers, cargo handlers and airlines can now identify the ULD’s classification and the owner at a glance.

The first three letters of a ULD code are perhaps the most important. They are used to identify the type, size and shape of the ULD. This information is vital in determining not only the type of cargo it can contain but also the aircraft it is compatible with.

The three-letter prefix works as follows:

The first letter represents the type of ULD

The second letter represents the base size of the ULD

The third letter represents the container’s contour or the pallet’s restraint system

What is Long Range Aid to Navigation System (LORAN) - Aircraft Navigation Basic Knowledge

The LORAN, or Long Range Navigation system was developed in the United States during World War II. It was similar to the British GEE system but used lower frequency radio waves to give it a longer range of as much as 1500 miles. This longer range also resulted in lower accuracies, in the order of 10's of miles, but this was deemed acceptable as it was decided that GEE could be used for short range navigation whilst LORAN would be utilized for longer range. LORAN was first used by ships and aircraft in the Atlantic theatre but eventually found more extensive use in the Pacific.

The accuracy was a function of the length of the line which connects the two stations and the distance between the ship and the stations. It remained in popular use until satellite navigation replaced it in the middle of the 80's, and in some places until the turn of the century.

The most recent edition, LORAN-C, has been very useful and accurate to aviators as well as maritime sailors. LORAN uses radio wave pulses from a series of towers and an on-board receiver/computer to positively locate an aircraft amid the tower network. There are twelve LORAN transmitter tower “chains” constructed across North America. Each chain has a master transmitter tower and a handful of secondary towers. All broadcasts from the transmitters are at the same frequency, 100 KHz.

Therefore, a LORAN receiver does not need to be tuned. Being in the low frequency range, the LORAN transmissions travel long distances and provide good coverage from a small number of stations.

Loran-C receivers combined two different techniques, multilateration and phase shift resulting in the capability to produce a highly accurate fix. The multilateration (or hyperbolic) navigation fix thus obtained was then further refined using measurement of the pulse phase difference between the station pairs.

**NOTE

Loran-C is a federally-provided radio navigation system for civil marine use in U.S. coastal areas. The Nation no longer needs this system because the federally-supported civilian Global Positioning System (GPS) has replaced it with superior capabilities. As a result, Loran-C, including recent limited technological enhancements, serves only the remaining small group of long-time users. It no longer serves any governmental function and it is not capable as a backup for GPS.

How do Jet engine works? (Basic)

1) Fan

The fan is located at the front of the engine and is the primary air intake. Large spinning blades suck in vast quantities of air, accelerating the gas and splitting it into two separate streams. Some of the air is directed around to the rear of the engine to produce thrust, while the rest is channeled into the engine’s core where it enters the next stage.

2) Compressor

The compressor squeezes the air drawn in by the fan blades, compressing it into a smaller volume and increasing the pressure. The compressor section is lined with multiple rows of blades that force the air into progressively smaller channels.

Compressing the air increases the potential energy, and concentrates the oxygen molecules for more efficient combustion in the next stage.

3) Combustor

The combustor introduces fuel into the compressed air and ignites the mixture, creating a high-pressure expanding gas. This is the hottest section of the engine, where energy is released from burning fuel and temperatures can climb over 2,000 degrees Fahrenheit.

The combustor is lined with fuel-injecting nozzles and an igniter to spark the reaction. Once ignition occurs, a steady stream of fuel ensures combustion is maintained, and the expanding gas is directed downstream into the turbine section.

4) Turbine

The turbine section is another series of rotating blades that are driven by high-pressure air leaving the combustor. The turbine blades catch the rapid airflow, and rotate to drive a spinning shaft that turns the fan and compressor at the front of the engine. The turbine essentially powers the rest of the engine, harnessing energy from the combustion chamber to maintain steady air intake and compression. Air passing though the turbine loses energy to the rotating blades, but what remains moves into the final exhaust stage of the engine where it is expelled to produce thrust.

5)Nozzle

The nozzle is the cone-shaped duct at the rear of the engine. Here the airflow from the engine core and the bypassed air from the fan section are expelled to produce thrust. The engine nozzle is usually tapered to accelerate the escaping gas, and the air exiting the nozzle exerts a force on the engine that propels the aircraft forward.

Some engines employ an afterburner to generate additional thrust. The afterburner injects more fuel and ignites the mixture after it has passed through the turbine.

The process significantly enhances the velocity of air exiting the nozzle, but it consumes excess fuel and is only employed for brief periods on specialized military aircraft.

Effects of overloaded Aircraft- Basic

1. Increased Take-off Speed

Increase in take-off speed because more lift is necessary to counter the additional weight, higher speed is necessary to create sufficient lift to attain flight. The reason why aircraft can fly because it produces high lift force. Thus, the heavier the aircraft the more power of lift need to be generated to lift the aircraft . Thus, higher take off speed is needed to produce huge amount of thrust which will create more lift.

2. Longer Take-off  Run

The increase in necessary speed for takeoff and slower acceleration due to increased weight translates to more runway required to accelerate the airplane to takeoff speed. Logically, overloaded aircraft need more time to reach take-off speed. More time needed means more distance or longer runway required to reach take-off speed. This is dangerous as if aircraft fail to reach take-off speed at available distance, the aircraft might crash with obstacles or overshoot the runway and crash.

3. Lower Cruising Speeds

Production of additional lift to counteract greater weight results in an increase in drag. This increased drag reduces the speed at which the aircraft travels.

4.Less Maneuverability

The heavier the airplane is, the less maneuverable it becomes.

This is so because the force necessary to change the speed or direction of an object in motion increases with the mass of the object.

**Maneuverability = aircraft ability to turn away from its previous path.

5. Reduced Landing Performance

Overloaded can cause higher approach and landing speeds are necessary. Higher landing speed thus lead to greater landing distance.

6. Aircraft Structure Damage

Although the primary concern of an overloaded airplane is its effect on aerodynamic performance, a secondary concern is its effect on structural components, such as landing gears. This is because, the landing gear could not support the weight of aircraft especially due to the impact during landing.

**Special Note

Items that contribute to weight changes:

-Fuel Load

-Cargo and Passenger

-Equipment and Modification

*Fuel Load

The operating weight of an aircraft can be changed by simply altering the fuel load. During flight, fuel burn is normally the only weight change that takes place. As fuel is used, an aircraft becomes lighter and performance is improved.

*Cargo & Passenger

This weight can’t be altered during flight. But we can monitor this weight before our journey.

*Equipment & Modification

Change of fixed equipment have a major effect upon aircraft weight. Installation extra radios or instrument may affect the weight. Aircraft modification and repairing may contribute to weight change.

Trimmable Horizontal Stabilizer Actuator

The design of the majority of airliners and transport aircraft incorporates a trimmable horizontal stabilizer. Like a stabilator, the trimmable stabilizer features a fully moving horizontal tail surface. However, unlike the stabilator, the trimmable stabilizer does not move in response to control column or control stick movement.

Instead, it is fitted with elevators which respond to pilot or autopilot input to control pitch and adjust the aircraft attitude and the entire horizontal tail assembly moves in response to the trim system to stabilize the aircraft in the pitch axis.

The trimmable stabilizer's primary advantage is that it provides tremendous trimming power over the full speed range of the airplane. The system also reduces drag as the stabilizer surface and the elevator are in alignment whenever the aircraft is in trim. The stabilizer trim is normally adjusted to compensate for centre of gravity position prior to takeoff to ensure optimum elevator effectiveness.

In most cases, a trimmable stabilizer is either manually or electrically controlled and hydraulically actuated. In some Fly-By-Wire equipped aircraft, the stabilizer automatically adjusts to a one G loading without the need for pilot action.

**Advantages:

The main advantage is smaller elevator deflection angles. This comes handy in two cases:

When high-lift devices are deployed, the center of pressure on the wing shifts backwards by up to a third of wing chord. Fowler flaps add wing area aft of the trailing edge, and slotted flaps are able to generate high suction peaks. The result is a massive change in trim, and the empennage now has to generate generous downforce.

Changing the lift on the empennage by elevator deflection alone will exceed the maximum practicable deflection angle and leave no margin for control. By adjusting the stabilizer incidence, the elevator can be held near its neutral position and has reserves for control.

In transsonic flight the elevator might not always have a linear characteristic. The contour break due to an elevator deflection induces shocks which in turn lead to flow separation which reduces the control effectivity and can even reverse the control characteristic.

Since the transition from subsonic to supersonic flight shifts the center of lift backwards, the empennage needs to add downforce when the aircraft accelerates in the transsonic speed range. An elevator deflection might not be able to produce the desired lift change, and only adjusting the stabilizer such that the elevator can be held neutral can restore trim and control effectiveness.

The required elevator deflection angles are smaller in case of trimmed aircraft and the system has full elevator deflection angles at extreme trim angles.

If the stabilizer is not trimmed, the (human or auto)pilot has to continuously adjust the controls to prevent the aircraft from pitching up or down more than required.

Aligning the elevator with the stabilizer reduces drag.

It allows for a wider range of c.g. movement compared to the elevator-trim tab system.

**NOTE

There are 3 reasons for the existence of a THS.

1) The large speed range of jet airplanes.

2) The large trim changes with changes in the wing configuration, slats flaps etc.

3) The large range of CENTER of GRAVITY that is possible.

To reduce the drag produced by the tailplane especially during cruise, thus improving range significantly.

Difference between Ailerons and rudder

Let's go through with this stuff!

Rudder and ailerons have different purposes and control rotation about two different axis, but their use is coordinated since a rotation about one axis induces a secondary rotation on the other one.

The rudder use is mostly to prevent unwanted yaw movement for safety and comfort, or to force yaw against the aircraft tendency to keep the aircraft facing the relative wind (e.g. for a cross-wind landing). See Understanding the use of rudder for a more comprehensive explanation.

A turn is performed using the ailerons, but for a non-small turn an adverse yaw opposite to the turn develops, the rudder is used to maintain the desired attitude and what is known as a coordinated turn.

When a yaw damper is available, coordinated turns can be conducted without pilot action on the rudder, as the yaw damper controls the rudder automatically.

When speed and altitude increase, using the rudder to turn around the yaw axis with the wings horizontal, tends to make the aircraft flies in crab in the same direction rather than to turn it. Turning this way would require a larger rudder area and would generate additional drag. So this is not the way an aircraft is steered in flight.

1) Yawing aligns the aircraft with the wind

Lowering the aileron on a wing makes it more efficient, it generates more lift and raises. But generating more lift also induces more drag.This drag in excess tends to slow the aircraft on the upper wing side. This creates an adverse yaw movement in the direction opposite to the one desired.The pilot uses the rudder to counter the adverse yaw and keep the fuselage axis facing the airflow, countering slip and skid effects. This is known as performing a coordinated turn.

2) Ailerons-rudder coordination

The amount of rudder to apply can be determined using (human senses and) different instruments, including the turn coordinator which is a sort of level usually associated with a bank or rate of turn indicator.When executing a coordinated level turn without wind, at sea level, etc, the radius of the turn and the turn rate depend only on the airspeed and the bank angle:Example:

TAS 150kt, bank 20°: Radius 1,676m, 360° in 2:16.

TAS 300kt, bank 30°: Radius 4,227m, 360° in 3:51.

**Note

Ailerons deflection reduced in the turn

Thus,when the desired bank angle is reached, the pilot reduces the ailerons deflection. The excess of lift and drag on the upper wing decreases too, as does the adverse yaw. The rudder deflection can be reduced too.

Normally the aircraft should maintain its bank and continue to turn with ailerons in neutral position, due to the upper wing flying faster and generating more lift.

However the aircraft in a rolled attitude actually slips into the turn and the dihedral effect tends to decrease the roll angle of the slipping aircraft (roll stability). So some degree of aileron deflection will be maintained. The ailerons (and the rudder) are used to return the wings to their horizontal position and stop the turn more accurately.

Ailerons are the primary surfaces used for turning an aircraft. Rudder is used only to correct the adverse yaw effect created during roll.

If a pilot uses, only rudder for turning then, the radius of a turn would become high, which is undesirable.

(many a times, aircrafts need to take high angle turns just after their take off. Imagine the radius/distance/time it would take for making a 60 degrees degrees turn)

Secondly while using only rudder, there is tendency of aircraft to roll, due to difference in relative speed on left and right wing). This roll amount is unpredictable and hence the use of only rudder for turning is avoided.

AIRPROX (Aircraft Proximity)

An Airprox is defined as 'a situation in which, in the opinion of a pilot or air traffic services personnel, the distance between aircraft, as well as their relative positions and speed, have been such that the safety of the aircraft involved may have been compromised.' 

ICAO defines a series of classifications for AIRPROX events which have been reported and subsequently investigated by an appropriate body. It is required that this classification should be assigned on the basis only of actual risk, not potential risk. This means that only the residual risk after any avoiding action is considered.

The available classification categories are:

A - Risk of collision. The risk classification of an aircraft proximity in which serious risk of collision has existed. An A AIRPROX may or may not be deemed to be a Serious Incident as defined by ICAO Annex 13.

B - Safety not assured. The risk classification of an aircraft proximity in which the safety of the aircraft may have been compromised.

C - No risk of collision. The risk classification of an aircraft proximity in which no risk of collision has existed.

D - Risk not determined. The risk classification of an aircraft proximity in which insufficient information was available to determine the risk involved, or inconclusive or conflicting evidence precluded such determination.

The definition and classification of an AIRPROX given above was agreed prior to the introduction of ground radar and airborne systems (ACAS) capable of measuring accurately the actual separation of the aircraft involved.

ICAO Emergency Phases

The Search and Rescue (SAR) function is a state obligation imposed by the Convention on International Civil Aviation (Chicago, 7 December 1944) which is generally referred to as the Chicago Convention. Annex 12 to the ICAO Chicago Convention defines three emergency phases which are referred to as the Uncertainty Phase, the Alert Phase and the Distress Phase. These phases are defined as follows:

**Uncertainty phase (INCERFA): a situation wherein uncertainty exists as to the safety of an aircraft and its occupants.

1) When communication from an aircraft has not been received within 15 minutes after the time a communication should have been received or after the time an unsuccessful attempt to establish communication with such aircraft was first made, whichever is earlier; or

2) When an aircraft fails to arrive within 30 minutes after the time of arrival last estimated by the pilot or by the ATC units, whichever is later.

**Alert phase (ALERFA): a situation wherein apprehension exists as to the safety of an aircraft and its occupants.

1) Following the uncertainty phase when subsequent attempts to establish communications with the aircraft, or inquiries to other relevant sources have failed to reveal any information about the aircraft; or

2) When information has been received which indicates that the operating efficiency of the aircraft has been impaired but not to the extent that a forced landing is likely; or

3) When communication from an aircraft has not been received within 30 minutes after the time a communication should have been received or after the time an unsuccessful attempt to establish communication with such aircraft was first made, whichever is earlier.

**Distress phase (DETRESFA): a situation wherein there is a reasonable certainty that an aircraft and its occupants are threatened by grave and imminent danger and require immediate assistance.

1) Following the alert phase when further attempts to establish communications with the aircraft and more widespread inquiries are unsuccessful; or

2) When the fuel on board is considered to be exhausted or to be insufficient for the aircraft to reach safety; or

When information is received which indicates that the operating efficiency of the aircraft has been impaired to the extent that a forced landing is likely; or

3) When information is received or it is reasonably certain that the aircraft is about to make or has made a forced landing.

Each State is responsible for developing and promulgating clear criteria for the declaration of each emergency phase. Air Traffic Services (ATS) or the responsible Rescue Coordination Centre (RCC), as appropriate, will make the Emergency Phase declaration within the timeframe specified for the trigger event. As an example, loss of radio contact with an aircraft under ATS control could result in declaration of the Uncertainty Phase within 10 minutes, the Alert Phase within 20 minutes and the Distress Phase within 30 minutes of the event whereas loss of radio contact with an aircraft not under ATS control might not trigger the Uncertainty Phase declaration until 30 minutes had elapsed with Phase upgrade occurring at 30 minute intervals.

Radio Frequency Interference (RFI) - Basic

“Radio Interference” is the term used to describe a range of different situations in which transmissions other than those from authorized users of an RTF frequency interfere with radio reception. Radio interference often comes from commercial stations on the ground.

Radio Frequency Interference (RFI), which is unwanted noise or signals being transmitted by some other installation on board and being received on the tuned frequency. Most likely source will be the engine ignition system, or another radio set which may have ‘un-clean’ emissions, or strobes or Transponders.

What are the effects?

- Interference can make communication difficult or even impossible, resulting in loss of communication.

- Increased pilot workload and ATCO workload.

- Callsign Confusion.

**Factors that contribute towards interference

- Weather.

For example the static generated in thunderstorm clouds.

- Atmospheric Conditions.

In unusual propagation conditions, especially high pressure situations, transmissions from authorized aeronautical transmitters using the same frequency may interfere with transmissions from stations which are well beyond the protected range.

-Unauthorized transmissions.

Interference may result when an unauthorized transmitter is established on a frequency close to the aeronautical frequency, or on one of its sub-harmonic frequencies.

- Malicious Transmissions.

There have been rare occasions when an unauthorized station has made malicious transmissions on an aeronautical frequency, presumably with the intention of misleading pilots. This form of interference is usually fairly obvious because the transmissions lack credibility due to their non-standard timing, content or form; however, such transmissions made at critical stages, e.g. during the take-off run, can have potentially very dangerous consequences.

What is Shimmy Dampers?

A shimmy damper uses a cylinder filled with hydraulic fluid or a rubber/lubricant combination to prevent rapid movement of the nosewheel, while not interfering with slower operations. The damper can be built integrally within the nose gear, but most often it is an external unit attached between the upper and lower shock struts. It is active during all phases of ground operation while permitting the nose gear steering system to function normally.

Shimmy happens as a result of any force that upsets aligned nose wheel rotation (i.e. nose wheel in line with the forward movement of the aircraft).

Nowadays, there are also fluid-free shimmy damper. Here the hydraulic fluid, is replaced and uses a rubber formulation with high-tech lubricant. Best part is that there’s no fluid to leak.

Pulse Light Approach Slope Indicator (PLASI)

A visual approach aid for use in visual flight conditions which assists the execution of a stabilised approach by transmitting visible beams up the approach from a position adjacent to the intended touchdown point of a runway or helipad rather like a PAPI. The PLASI is a Visual Glide Slope Indicator (VGSI) and is similar to the VASI systems located at most commercial airports with on important exception:

1) The PLASI System is more precise and easier for pilots to identify the actual projected glide path.

2) The PLASI system provides the pilot with a stabilized approach by means of a single light signal from a location near the intended touchdown point on the runway.

A PLASI system usually has an effective visual range of 5 nm during the day and up to 20 nm at night. When on the correct vertical profile, a steady white light will be seen, if above it, the white light will flash and if below it, a steady red light will show. This red light will begin to flash when much too low. Suitably configured PLASI systems may be used to assist either fixed wing or rotary wing approaches.

Level Bust (Altitude Deviation)

An altitude deviation ( referred as level bust ) is defined by regulations as an unauthorized deviation from the assigned altitude ( or flight level ) equal to or greater than 300 ft ( 200 ft in RVSM airspace ).

This also includes the failure to capture the assigned altitude / flight level ( i.e., overshoot or undershoot of the cleared altitude / flight level ).

A Level Bust or Altitude Deviation occurs when an aircraft fails to fly at the level to which it has been cleared, regardless of whether actual loss of separation from other aircraft or the ground results.

Level busts are becoming less dangerous because improvements in technology such as better STCA and Mode S have improved the ability of controllers to safely manage any consequent loss of separation. Furthermore, the availability and proper use of ACAS provides a final safety net which significantly reduces the risk of a Mid-Air Collision, and TAWS has also reduced the risk of a level bust resulting in a CFIT accident.

Altitude deviations may result in :

• A loss of separation

• A midair collision

• A CFIT event

*Types of altitude deviation are:

1) The controller assigns an incorrect altitude or reassigns a flight level after the flight crew have been cleared to an altitude.

2) Breakdown the pilot-controller communication.

3) The flight crew accepts an altitude clearance meant for another aircraft (call sign confusion).

4) The flight crew accepts, understands and reads back the cleared altitude but set the wrong altitude due to distractions/interruptions

failure by the other pilot to cross check the set altitude.

5) The autopilot fails to capture the selected altitude. This normally happens because of the late selection of the autopilot coupled with the high rate of climb.

6) The tunnelling effect where the flight crew fails to respond to altitude alert aural and visual warning when hand flying.

7) The flight crew conducts an incorrect go around procedure.

Low transition altitude , with low/high QNH.

8) Technical fault of the aircraft which fails to alert the flight crew of an altitude bust.

9) The misunderstanding of altitude clearances due to the speed and use of non standard phraseology.

10) Complex and long instructions with multiple clearances issued on the same transmission.

*Factor that contribute to altitude bust:

1) Distraction/ interruption during the transmission and selection of altitude.

2) high workload –ATCO and flight crew

3) poor design of airspace procedures- misunderstanding of the information presented.

4) holding patterns

5) high traffic volume

6) rate of climb/descend which are high

**Note

Altitude deviations ( also referred to as level busts ) may result in substantial loss of vertical separation and/or horizontal separation, which could cause a midair collision.

What is Runway Status Lights (RWSL)?

Runway Status Lights is a fully automatic, advisory system designed to reduce the number and severity of runway incursions and prevent runway accidents while not interfering with airport operations. It is designed to be compatible with existing procedures and is comprised of Runway Entrance Lights (RELs) and Takeoff Hold Lights (THLs).  Runway Intersection Lights (RILs) were subsequently added and now the intention is to integrate the three RWSL elements with the Final Approach Runway Occupancy Signal (FAROS) system which will provide runway occupancy alerting to aircraft on final approach indicating that it is unsafe to land by automatically changing the PAPIs from a steady illumination to an intermittent one.

The FAA developed Runway Status Lights as part of an ongoing effort to explore new technologies. The system aims to improve air crew and vehicle operator situational awareness through accurate and timely indication of runway usage.

RWSL and any similar systems are generically identified by ICAO as Autonomous Runway Incursion Warning Systems (ARIWS). Specifications for such systems are provided in Annex 14.

3 principles of RWSL:

1) RELs warn that it is unsafe to enter/cross a runway

The Runway Entrance Lights system is composed of flush mounted, in-pavement, unidirectional fixtures that are parallel to and focused along the taxiway centerline and directed toward the pilot at the hold line. A specific array of Runway Entrance Lights lights include the first light at the hold line followed by a series of evenly spaced lights to the runway edge; and one additional light at the runway centerline in line with the last two lights before the runway edge. When activated, these red lights indicate that there is high speed traffic on the runway or there is an aircraft on final approach within the activation area.

2) THLs warn that it is unsafe to take off from a runway

The Takeoff Hold Lights system is composed of in-pavement, unidirectional fixtures in a double longitudinal row aligned either side of the runway centerline lighting. Fixtures are focused toward the arrival end of the runway at the "line up and wait" point, and they extend for 1,500 feet in front of the holding aircraft. Illuminated red lights provide a signal, to an aircraft in position for takeoff or rolling, that it is unsafe to takeoff because the runway is occupied or about to be occupied by another aircraft or ground vehicle. Two aircraft, or a surface vehicle and an aircraft, are required for the lights to illuminate. The departing aircraft must be in position for takeoff or beginning takeoff roll. Another aircraft or a surface vehicle must be on or about to cross the runway.

3) RILs warn that it is unsafe to cross a runway intersection

RILs are the third component of the RWSL system and were first installed for operational evaluation at Boston in 2010. They are used where one runway intersects another and provide an indication to pilots and vehicle drivers that there is high speed traffic on the intersecting runway and that it is unsafe for to enter or cross. They consist of red unidirectional lights installed in a double longitudinal row aligned with and offset to either side of the runway centerline lighting in the same manner as and using the same light fixtures as THLs.

**How RWSL Works

The system determines the locations of aircraft and vehicles on the airfield, as well as of departing and arriving aircraft using data from three surveillance sources:

A) Surface primary radar returns from the Airport Surface Detection Equipment (ASDE).

Multi-lateration calculated from the differences of time of arrival of transponder signals from aircraft and vehicles; data from several multi-lateration receiver locations are used.

C) Airport Surveillance Radars for aircraft operating in the vicinity of the airport.

Basic on Turboprop Engine

A turboprop engine is a variant of a jet engine that has been optimized to drive a propeller. Turboprop equipped aircraft are very efficient at lower flight speeds (less than mach 0.6), burning less fuel per seat-mile and requiring significantly less runway for takeoff and landing than a turbojet or turbofan powered aircraft of the same size. When the aircraft is used over relatively short distances, these cost and performance benefits offset the lower speed making turboprops the engine of choice for most commuter aircraft.

A turboprop engine uses the same principles as a turbojet to produce energy, that is, it incorporates a compressor, combust and turbine within the gas generator of the engine. The primary difference between the turboprop and the turbojet is that additional turbines, a power shaft and a reduction gearbox have been incorporated into the design to drive the propeller. The gearbox may be driven by the same turbines and shaft that drive the engine compressor, mechanically linking the propeller and the engine, or the turbines may be separate with the power turbine driving a concentric, mechanically isolated shaft to power the gearbox.

The latter design is referred to as a "free power turbine" or, more simply, a "free turbine" engine. In either case, the turbines extract almost all of the energy from the exhaust stream using some of it to power the engine compressor and the rest to drive the propeller.

Aircraft powered with turboprop engines go significantly faster than aircraft with propellers powered by reciprocating engines but not as fast as pure jet aircraft. Operating costs for turboprop planes are often one tenth the costs for turbojet powered planes.

Turboprop aircraft are generally used for shorter length flights than pure jets. They are efficient at lower altitudes and lower airspeed than pure jets. They are generally smaller in terms of seats and cargo capacity but have a wide range of sizes from a few seats to perhaps a hundred. Turboprops also can operate from shorter runways than pure jets with similar payload capacities. That means they are ideal for some military applications where the C-130 has been a work horse for many decades.

**Note

Turboprop engines (AKA turboshaft engines) use the same basic turbine arrangement as a turbojet engine but are optimized to generate torque on a central shaft instead of maximizing thrust generated by the air/fuel flow in the engine. The shaft is connect to an otherwise normal propeller to provide most of the thrust to make an aircraft fly. In the case of helicopters the same type of engine is used to turn the main rotors and provide lift. These engines produce generally less power than fan jet engines but are much more efficient while producing this lower level of power.