Meteorology

Wind factor (Aircraft Performance) - Basic

Most aircraft accidents occur during the take-off and landing phase of the flight. Collisions with obstacles during climb out, runway overruns on landing occur every now and then. On this section of the site we will take a look at the various factors contributing to the performance of the aircraft in this part of the flight. Hopefully we help the pilot ensuring safe operation during these phases of the flight as the rules require that of the pilot in command.

The effect of wind has on our aircraft is something we can influence to some extend. We can choose runways with the greatest headwind component (when the airport has more than one runway) and use the wind on our tails when flying to our destination. Windspeed and direction usually changes with altitude so that effect can be used too.

The last part of the flight (landings) can be the most demanding for the pilot, and during training he/she will spend a lot of time practicing these to almost perfection.

1) Headwinds & Tailwinds

Aircraft use the flow of wind over the wings to generate lift to be able to fly. A minimum amount is required to lift-off and usually the engine generates thrust to obtain this lift-off speed.

*Headwind

By taking off into the wind (the wind will generate part of the required lift) the aircraft lifts off sooner and this will result in a lower ground speed and therefore a shorter take-off run for the aircraft to become airborne. It is therefore recommended.

Not only for safety reasons: a take-off that is abandoned will also use less runway to stop because ground speed is lower (check the ASDA distance during preflight). Climbing into the wind will result in a steeper climb, which is ideal for clearing obstacles in your climb out path.

Landing into the wind has the same advantages, it uses less runway, ground speed is lower at touchdown (less wear and tear on the aircraft) and the runway is available sooner for the next aircraft when it gets a bit crowded.

A rule of thumb says that take-off and landing distances are reduced 1,5 % for each knot of headwind up to 20 knots.

*Tailwind

Take-offs with a tailwind will result in the use of much more runway to get enough lift for flight (It takes distance to nullify the tailwind before any headwind is obtained for lift). Climb angle is also reduced. Think about obstacles! A five knot tailwind increase take-off distance with 25% and a ten knot tailwind with about 55%.

The same can be said about landing distances. The main reasons for executing tailwind operations could be airport noise abatement procedures or commercial operations and in case of certain mountain airports where you land up slope and take-off down slope again.

**Landing

Landing with a tailwind has another problem: you will approach the runway with a higher ground speed and this could lead the pilot into lowering his airspeed because he/she is visually accustomed to a lower ground speed. At this point a stall can happen, with no room to recover from it. But the solution is simple: be aware of this problem and concentrate a bit more and fly your usual indicated final approach speed and expect to use more runway.

During landing the best thing to do is to avoid tailwinds altogether, only if sufficient runway and pilot experience is available it can be done safely.

Remember: tailwinds do not lower the indicated airspeed or stall speed, they influence the ground speed of the aircraft.

**Turbulent Gusting Winds

Aircraft Performance, Tailwind

On take-off with gusting winds it will be required that you keep the aircraft on the ground somewhat longer to provide a higher margin from the stall. During landing you must add half the gust factor to your final approach speed. Thus if tower reports the wind 240 at 18 gusts 28 it is advisable to add 5 kts to your airspeed.

**Gust Factor

It is wise to do the same on take-off. Add half the gust factor to your normal lift-off speed, this should provide a safe margin from the stall. Keep in mind that because of these higher take-off and approach speeds more distance on the runway is required so with short runways this technique may not be ideal.

Formation of Wave drag

Wave Drag is a force, or drag, that retards the forward movement of an airplane, in both supersonic and Transonic Flight, as a consequence of the formation of shock waves. 

Wave drag is caused by the formation of shock waves around the aircraft in supersonic flight or around some surfaces of the aircraft whilst in transonic flight. Whilst in cruise, most civil jet aircraft fly in the mach .75 to .85 speed range. Although shock waves are typically associated with supersonic aircraft, they also form on an aircraft traveling at less than the speed of sound on areas of the aircraft, such as the aerofoils, where local airflow is accelerated to sonic speed and then decelerated, once again, back to subsonic speed. The shockwave (and associated wave drag) forms at the point the airflow becomes subsonic. As the aircraft continues to accelerate, the area of the wing experiencing supersonic flow increases, the shockwave moves further back on the wing and becomes larger. Boundary layer separation also increases with the increase in speed and if the speed is allowed to increase beyond the limiting mach number (MMO), severe buffeting, Mach Tuck, or "upset" (loss of control) may occur.  

Most modern jet powered aircraft are engineered to operate at transonic air speeds. Transonic airspeeds see a rapid increase of drag from about Mach 0.8, and it is the fuel costs of that drag that typically limits the airspeed. Attempts to reduce wave drag can be seen on all high-speed aircraft; most notable is the use of swept wings, but another common form is a wasp-waist fuselage as a side effect of the Whitcomb area rule.  

*Note

Shock wave formation causes an increase in drag. One of the principal effects of a shock wave is the formation of a dense high pressure region immediately behind the wave. The instability of the high pressure region, and the fact that part of the velocity energy of the airstream is converted to heat as it flows through the wave, is a contributing factor in the drag increase, but the drag resulting from airflow separation is much greater. If the shock wave is strong, the boundary layer may not have sufficient kinetic energy to withstand airflow separation. The drag incurred in the transonic region due to shock wave formation and airflow separation is known as “wave drag.” When speed exceeds the critical Mach number by about 10 percent, wave drag increases sharply. A considerable increase in thrust (power) is required to increase flight speed beyond this point into the supersonic range where, depending on the airfoil shape and the AOA, the boundary layer may reattach. 

Difference between Outside air temperature (OAT) or Static air temperature (SAT)  and  Total Air Temperature (TAT) - Basic

The temperature of the air outside an aircraft is measured and indicated within the cockpit or used, together with outputs from the Pitot Static System, as an input to aircraft equipment, e.g. Air Data Computer (ADC).

Outside air temperature, or OAT, is the only temperature used in general aviation. This temperature is referred to as SAT or static air temperature in jet aircraft. TAT, or total air temperature, is the measurement of the effective air temperature caused by the effects of friction. The higher the airspeed, the greater the difference between SAT and TAT. 

The ambient temperature measured outside an aircraft is known as the Outside Air Temperature (OAT) or Static Air Temperature (SAT). The sensor which detects OAT must be carefully sited to ensure that airflow over it does not affect the indicated temperature.  

If temperature is measured by means of a sensor positioned in the airflow, kinetic heating will result, raising the temperature measured above the OAT. The temperature measured in this way is known as the Total Air Temperature (TAT) and is used in ADCs to calculate True Airspeed (TAS). Careful design and siting of the TAT probe is necessary to ensure accurate measurement of TAT.

Fuel Gravity

Fuel gravity is a measurement of its density relative to air temperature. The measurement is based on a standard measurement. The standard measurement is based on a sea level temperature of 60 Degrees F and measured against the same volume as water at SL and Temperature. At 60 F at Sea level, one US gallon of Jet A fuel weighs 6.78 lbs while a gallon of water weights 8.35 lbs. To determine fuel gravity, you divide the Jet fuel weigh by the water weight, in this case, the gravity weight is .81 not including any fuel additives that may or may not be present. In the old days, we used to order fuel with Prist, (when required) an additive sort of like antifreeze, that prevented ice from clogging fuel lines between the tanks and the turbines. Adding it changes the fuel gravity and the overall fuel weight. (I’m not even sure if its used anymore, or replaced with a different type of additive). Once the fuel weight is determined, the known fuel weight order can be calculated and converted into a volume measurement. Many modern airliners have fuel heaters built into the tanks, eliminating the need for the additive.

If the specific gravity calculation is out of specification, it helps determine if there is a contamination, human, mechanical or calculation error. Fuel weight is based on the specific gravity number to calculate its weight on actual air temperature. This determines gross take off weight and quantity of the fuel in the aircraft tanks. Fuel volume is dense in cold environments and expansive when warm. Any discrepancy between the refueling tanker volume gauges and what is indicated on the cockpit fuel gauges must be also determined. A -/+ 2 percent variance was acceptable back in my day. If it is calculated to be out of that range, something is wrong. Usually it is a case of not enough or too much fuel being loaded. I had only two occasions when such an occurrence happened. Both times I had the fuel tanks manually dipped to verify how much fuel was on board. On both occasions more fuel was loaded than what we asked for. One was the refueling operator made the error and misread the ticket quantity relative to what he actually loaded aboard. The second one was more problematic for the fuel company as it was determined that their fuel flow meters were no longer accurate and out of specification. Fuel had to be offloaded as we determined we were over maximum gross take off weight with the fuel that was loaded. We were then refueled in incremental steps with the tanks manually dipped to determine actual fuel quantity aboard.

Older jet turbines were more susceptible to poor performance if the fuel gravity was out of specification. Jet fuel was / is available in a variety of blends as I described earlier but has nothing to do with its actual fuel gravity calculation. Like automotive fuels, the reason for different types is to accommodate environmental conditions and turbine requirements. There used to be 5 to 6 different grades of Jet Fuel in addition to military spec. Some fuels had higher blends of additives / detergents to prevent algae from growing in the fuel tanks. Additives must be taken into account to determine the actual fuel load weight.

Another reason specific fuel gravity is important is for use by the refueler operator mentioned above. The refueling tanker quantity gauges are by volume, not weight. In the U.S., it’s US gallons while in Canada and every other nation, it’s liters. The refueler will calculate the amount of fuel requested by using its gross weight divided by the gravity fuel number to determine the volume of fuel to load aboard the aircraft. Today, the process is identical, but the fuel is delivered by an underground network of pipes with fuel connection points built into the tarmac of the parking stand at most modern airport gates. The refueling weight procedure used to be known as the amount of fuel volume uplift delivered by the operator. I think it still is, been a long time since I’ve ordered 20,000 gallons of Jet A.

Types of Clouds

Clouds are made up of very light water droplets or ice crystals. These particles can float in the air. When warm air rises, swells and cools, it forms clouds. Many water droplets formed together scatter reflect sunlight and you see a white could, but with a dark or gray cloud, the sunlight is scattered in all directions instead of reflected. The different types of clouds are cumulus, cirrus, stratus and nimbus.

Cirrus Clouds

Cirrus clouds are the thin, wispy clouds seen high in the sky. They look as if someone took a cloud, stretched it, pulling pieces off, like a cotton ball when it is pulled apart. They are thin because they are made of ice crystals instead of water droplets. A blue sky and a few cirrus clouds high in the sky, usually means it is going to be a nice day.

Cumulus Clouds

Cumulus clouds are the puffy clouds that are usually scattered throughout the sky. In Latin, the word cumulus means pile. Just like when we say “accumulate,” it means things pile up. This type of cloud is formed when warm air rises carrying water vapor with it by evaporation. Cumulus clouds can be white or gray. White fluffy clouds means no rain, but when they form into dark or gray clouds, it is going to rain.  Cumulus clouds have sharp outlines and a flat base at a height of 1000m. 

Cirrocumulus clouds are small rounded puffs that usually appear in long rows high in the sky. Cirrocumulus are usually white, but sometimes appear gray. They are the same size or smaller than the width of your littlest finger when you hold up your hand at arm's length. When these clouds cover a lot of the sky, they can look like the scales of a fish, which is it is called a "mackerel sky.” Cirrocumulus are common in winter and indicate fair, but cold, weather. 

Cirrostratus clouds are high, thin sheet-like thin clouds that usually cover the entire sky. The clouds are so thin that the Sun or moon can sometimes shine through and appear to have a halo as light hits the ice crystals and bends. The halo is the width of your hand held at arm's length. Cirrostratus clouds usually come 12 to 24 hours before a rain or snowstorm. 

Stratus Clouds

Stratus clouds look like a huge thick blanket covering the sky. These clouds are a sure sign of rain if it is warm and snow if it is cold. If stratus clouds are near the ground, they form fog. These clouds form when the weather has been cold and warmer moist air blows in. The amount of moisture in the air and the difference between warm and cold air determine how thick the cloud or fog is.

Nimbus Clouds

The word nimbus means a cloud that already has rain or snow falling from it. These clouds are dark and seen during a thunderstorm along with thunder and lightning. They can be a combination of two clouds, like a cumulonimbus, which means a puffy black cloud with rain falling out or it, or a stratonimbus, which is a dark blanket with rain falling out of it.

Cumulonimbus clouds also have vertical growth and can grow up to 10 km high. At this height, high winds will flatten the top of the cloud out into an anvil-like shape. Cumulonimbus clouds are thunderstorm clouds and are associated with heavy rain, snow, hail, lightning, and sometimes tornadoes. 

Altocumulus clouds are mid-level, grayish-white with one part darker than the other. Altocumulus clouds usually form in groups and are about one kilometer thick. Altocumulus clouds are about as wide as your thumb when you hold up your hand at arm's length. If you see altocumulus clouds on a warm, humid morning, there might be a thunderstorm by late afternoon.

Altostratus clouds are mid-level, gray or blue-gray clouds that usually covers the whole sky. The Sun or moon may shine through an altostratus cloud, but will appear watery or fuzzy. If you see altostratus clouds, a storm with continuous rain or snow might be on its way. Occasionally, rain falls from an altostratus cloud. If the rain hits the ground, then the cloud has become a nimbostratus. 

Mammatus clouds are pouches of clouds that hang underneath the base of a cloud. They are most often associated with cumulonimbus clouds that produce very strong storms. These clouds usually form during warm months, and are formed by descending air in the cloud. Mammatus clouds are sometimes described as looking like a field of tennis balls or melons, or like female human breasts. In fact, the name "mammatus" comes from the Latin word mamma, or breast. 

Lenticular, or lee wave, clouds form downwind of an obstacle in the path of a strong air current. In the Boulder, Colorado area, the obstacle is the Front Range of the Rocky Mountains, seen at the bottom of the picture. Wind blows most types of clouds across the sky, but lenticular clouds seem to stay in one place. Air moves up and over a mountain, with the lenticular cloud forming just past the mountaintop. The cloud evaporates on the downwind side, so it appears stationary even though air is moving through the cloud. Lenticular clouds are lens-shaped and often look like flying saucers.  

Kelvin-Helmholtz clouds look like breaking waves in the ocean. After wind blows up and over a barrier, like a mountain, the air continues flowing through the atmosphere in a wavelike pattern. Complex evaporation and condensation patterns create the capped tops and cloudless troughs of the waves. These clouds form when there is a difference in the wind speed or direction between two wind currents in the atmosphere. 

What is Ceiling?

The height above the ground or water of the base of the lowest layer of cloud below 6000m (20000ft) covering more than half of the sky (BKN or OVC).  This height is measured at automated weather stations (AWOS) by a very expensive device called a ceilometer. The ceilometer sends a laser beam upwards every 15 seconds. This laser determines the cloud height. The cloud height is recorded in feet above ground level. Usually in intervals of 100 feet. High clouds above 10,000 feet are recorded in thousands of feet above ground level. Most ceilometers detect clouds up to 12,000 ft. Some can detect clouds as high as 32,000 feet.  

The main difference between service and cruise ceilings is the aircraft rate of climb at those altitudes. At service ceiling, the rate of climb is 100 fpm. The service ceiling is the altitude at which the aircraft is unable to climb at a rate greater than 100 feet per minute (fpm).The cruise ceiling, on the other hand, is the altitude at which the maximum climb rate is 300 fpm, though I've not seen it used much. The absolute ceiling is the maximum altitude where the aircraft can sustain level flight. 

ATIS, AWOS, ASOS

ATIS (Automatic Terminal Information Service) is a recording that some airports broadcast in order to reduce frequency congestion. Current weather information, active runway information, NOTAMs, and other useful pieces of information are included in the ATIS. The ATIS is usually updated every hour or when there is a sudden weather change at the airport.   ATIS is traditionally a voice recording of someone reading the weather. D-ATIS is a way to deliver the information digitally so onboard equipment can interact with it.

Digital ATIS is an enhancement of the Tower Data Link Service (TDLS) and uses the Pre-Departure Clearance (PDC) System microcomputer to automate the delivery of airport and terminal area operational and meteorological information to aircraft flightcrews. Two phases of development are planned. The first phase will provide, via data link, a digital version of the ATIS /4 to flightcrews. Voice recording will continue to be utilized in the preparation of the ATIS broadcast. The second phase will add automated voice generation for the ATIS broadcasts

It will always give you the following information:

**ASOS

The ASOS systems are mostly operated and controlled by the NWS, DOD and sometimes the FAA. They help the national weather system compile data on the entire United States, not just for aviation purposes.

ASOS provides continuous observations necessary to generate a routine weather report (metar). They're more sophisticated than AWOS and designed to provide the necessary information to generate weather forecasts (TAF). ASOS is composed of a standard suite of weather sensors. 

They almost always have a basic level comparable to AWOS-III which means they can tell barometric pressure, wind speed and direction, DA, visibility, sky condition, ceiling height, and precipitation.


**AWOS

Automated weather observing system. A suite of weather sensors of many different configurations either procured by the FAA or purchased by individuals, groups or airports that are required to meet FAA standards. AWSS — automatic weather sensor system — is functionally the same as ASOS. AWOS can also generate automated remarks about density altitude, variable winds and ceilings. 

Do you know what a jet stream is?

Jet Stream is defined as a flat tubular current of air, quasi-horizontal, whose axis is along a line of maximum speed and which is characterised not only by great speeds but also by strong transverse (horizontal and vertical) gradients of speed (World Meteorological Organisation).

It is a strong current of air thousands of miles long, hundreds of miles wide , and several miles deep. Jet streams are found in the upper atmosphere, usually above 32,000 feet.

Meteorologists (scientists who study weather and climate in the atmosphere) know that jet streams can travel at hundreds of miles an hour. They were discovered toward the end of World War II by American bomber pilots over Japan and by German reconnaissance aircraft over the Mediterranean.

Meterologists also know that there are two main causes of jet streams:

The first main cause is that the hot air of the tropics rises and moves from the equator toward the North and South Poles. The warm air is pulled toward the cold air just the way steam always rises.

The second main cause is that while warm air is moving north and south to the poles from the tropics, the earth is also rotating on its axis from west to east. This west-to-east circulation of the earth creates a gigantic cross-current motion that ''bumps'' into the north-south moving air. It is at the bumping points where the jet streams begin.

Because of their strong winds, jet streams play an important role in the economy of the aviation industry. When an airplane flies into a jet stream for any period of time, extra fuel must be used. Not only is the fuel expensive, but it takes up room where either passengers or cargo could be. Just the opposite occurs when an airplane flies with a jet stream at its back. Fuel and money are saved because the wind pushes the plane along.

If you have ever flown in an airplane, you probably have experienced something called turbulence. Turbulence causes the bouncing, shaking feeling of the airplane. It means winds of different velocities (speeds) are buffeting the airplane. Besides a local weather storm, turbulence to an airplane may be caused by a plane flying into or out of a jet stream.

The turbulence caused by a jet stream occurs at the very edges of the jet stream, where the high-speed winds (over 200 miles per hour and sometimes all the way up to 300 m.p.h. over Japan) pass through the surrounding slower-moving air.

Just think of your plane as a canoe shooting down a river, only the water is wind in the sky. If a river is deep and straight, the water will run smooth and without waves even if the current is strong. Wherever the river bends and curves and the main currrent meets slower moving backwater rapids, or white water, occurs. This will cause your canoe to bounce around. This is exactly what happens to an airplane in the jet stream.

The wind currents along the edges of the jet stream are choppy or turbulent as high-speed air meets more slowly moving, nearly stationary air (about 20 m.p.h.). When a plane flies through this it bounces around. And since jet streams snake all over the sky, a plane can fly in an out of the turbulence many times in a single trip. To avoid turbulence pilots will fly to higher or lower altitudes to get beneath or above the jet stream.

Atmosphere- Basic

The atmosphere is a blanket of air made up of a mixture of gases that surrounds the Earth and reaches almost 350 miles from the surface of the Earth. This mixture is in constant motion. The atmosphere absorbs energy from the sun, recycles water and other chemicals, and works with the electrical and magnetic forces to provide a moderate climate. The atmosphere also protects life on Earth from high energy radiation and the frigid vacuum of space.

Because the Earth spins on its axis, and because the surface temperature is greater at the equator than at the poles, the atmosphere extends further out into space at the equator than at the poles. Air Density decreases with increasing altitude.

The atmosphere is divided vertically into five regions:

1) Troposphere

2) Stratosphere

3) Mesosphere

4) Thermosphere

5)  Exosphere

The boundary between the troposphere and the stratosphere is known as the Tropopause.

Most light aircraft and turboprop aircraft fly within the troposphere and this is where most of the water vapour and therefore cloud formation exists. Many types of jet aircraft are able to cruise in the Stratosphere, especially in high latitudes where the Tropopause is lower, thereby avoiding almost all weather - although some particular vigorous thunderstorms may penetrate the stratosphere.

a) Temperature falls with height in the troposphere but is generally constant at about -57°C in the stratosphere.

b) Considerable vertical movement of air occurs in the troposphere - warm air rising and cool air descending. This vertical movement is a direct consequence of Solar Heating.

Kindly go through with the sources given below for more information and better understanding about Atmosphere.


Gradual depressurization

A gradual (or subtle) depressurization occurs over a long period time and, due to the gradual change in air pressure, it can be difficult to recognize before cabin altitude warning devices activate or oxygen masks fall from the cabin ceiling.

Gradual depressurization will usually occur due to a leak in the aircraft pressure vessel, a malfunctioning outflow valve or a reduction in the cabin air inflow due to a malfunctioning compressor or other component. In addition to a gradual loss of cabin air pressure, there have been cases of aircraft failing to pressurize after takeoff, either due to equipment malfunction or incorrect manipulation of the pressurization controls. If this is not detected and corrected by the flight crew before the aircraft reaches cruising altitude, the lack of pressurization can also be difficult to recognize and may result in incapacitation due to Hypoxia.

With gradual depressurization, people aboard a plane can succumb to oxygen deprivation and cold if action is not taken quickly. For this reason, a reduction in altitude is usually the first course of action to ensure the crew and passengers’ safety.


ICING

Rain, snow, and ice are transportation’s longtime enemies. Flying has added a new dimension, particularly with respect to ice. Under certain atmospheric conditions, ice can build rapidly on airfoils and air inlets. On days when there is visible moisture in the air, ice can form on aircraft leading edge surfaces at altitudes where freezing temperatures start. Water droplets in the air can be supercooled to below freezing without actually turning into ice unless they are disturbed in some manner. This unusual occurrence is partly due to the surface tension of the water droplet not allowing the droplet to expand and freeze. However, when aircraft surfaces disturb these droplets, they immediately turn to ice on the aircraft surfaces. 


The two types of ice encountered during flight are clear and rime. Clear ice forms when  the remaining liquid portion of the water drop flows out over the aircraft surface, gradually freezing as a smooth sheet of solid ice. Formation occurs when droplets are large, such as in rain or in cumuliform clouds. Clear ice is hard, heavy, and tenacious. Its removal by deicing equipment is especially difficult. Rime ice forms when water drops are small, such as those in stratified clouds or light drizzle. 


The liquid portion remaining after initial impact freezes rapidly before the drop has time to spread over the aircraft surface. The small frozen droplets trap air giving the ice a white appearance. Rime ice is lighter in weight than clear ice and its weight is of little significance. However, its irregular shape and rough surface decrease the effectiveness of the aerodynamic efficiency of airfoils, reducing lift and increasing drag. Rime ice is brittle and more easily removed than clear ice. 


Mixed clear and rime icing can form rapidly when water drops vary in size or when liquid drops intermingle with snow or ice particles. Ice particles become imbedded in clear ice, building a very rough accumulation sometimes in a mushroom shape on leading edges. Ice may be expected to form whenever there is visible moisture in the air and temperature is near or below freezing. An exception is carburetor icing, which can occur during warm weather with no visible moisture present. 


Ice or frost forming on aircraft creates two basic hazards: 


1. The resulting malformation of the airfoil that could decrease the amount of lift. 


2. The additional weight and unequal formation of the ice that could cause unbalancing of the aircraft, making it hard to control. Enough ice to cause an unsafe flight condition can form in a very short period of time, thus some method of ice prevention or removal is necessary. 


Ice Prevention 


Several means to prevent or control ice formation are used in aircraft today: 


1. Heating surfaces with hot air 


2. Heating by electrical elements 


3. Breaking up ice formations, usually by inflatable boots 


4. Chemical application 


Equipment is designed for anti-icing or for deicing. Anti-icing equipment is turned on before entering icing conditions and is designed to prevent ice from forming. Asurface may be anti-iced by keeping it dry, by heating to a temperature that evaporates water upon impingement, or by heating the surface just enough to prevent freezing, maintainingit running wet. Deicing equipment is designed to remove ice after it begins to accumulate typically on the wings and stabilizer leading edges. 


Icing Effects 


Ice buildup increases drag and reduces lift. It causes destructive vibration and hampers true instrument readings. Control surfaces become unbalanced or frozen. Fixed slots are filled and movable slots jammed. Radio reception is hampered and engine performance is affected. Ice, snow, and slush have a direct impact on the safety of flight. Not only because of degraded lift, reduced takeoff performance, and/ or maneuverability of the aircraft, but when chunks break off, they can also cause engine failures and structural damage. Fuselage aft-mounted engines are particularly susceptible to this foreign object damage (FOD) phenomenon. 


Wing mounted engines are not excluded however. Ice can be present on any part of the aircraft and, when it breaks off, there is some probability that it could go into an engine. The worst case is that ice on the wing breaks off during takeoff due to the flexing of the wing and goes directly into the engine, leading to surge, vibration, and complete thrust loss. Light snow that is loose on the wing surfaces and the fuselage can also cause engine damage leading to surge, vibration, and thrust loss.


Whenever icing conditions are encountered, the performance characteristics of the airplane deteriorate. Decreased rate of climb must be anticipated, not only because of the decrease in wing and empennage efficiency but also because of the possible reduced efficiency of the propellers and increase in gross weight. Abrupt maneuvering and steep turns at low speeds must be avoided because the airplane stalls at higher-than-published speeds with ice accumulation. 


On final approach for landing, increased airspeed must be maintained to compensate for this increased stall speed. After touchdown with heavy ice accumulation, landing distances may be as much as twice the normal distance due to the increased landing speeds. In this chapter, ice prevention and ice elimination using pneumatic pressure, application of heat, and the application of fluid is discussed. 


The ice and rain protection systems used on aircraft keep ice from forming on the following airplane components: 


• Wing leading edges 


• Horizontal and vertical stabilizer leading edges 


• Engine cowl leading edges 


• Propellers 


• Propeller spinner 


• Air data probes 


• Flight deck windows 


• Water and waste system lines and drains 


• Antenna 

Contrail and Chemtrail 

Definition of a contrail: 


A contrail occurs when a plane travels at a high altitude (about 30,000 ft. or more) and compresses the air into a water vapor or ice crystals through jet engines or the wing tips pushing through the air. This trail disappears after a minute or so due to evaporation, because it's water. 


Definition of a chemtrail: 


The term "chemtrail" is a relatively new word, which appearedin the last few years along with the appearance of chemtrails. A chemtrail is very different from a contrail. At first a chemtrail might look a bit like a contrail. However, instead of disappearing like a contrail does, a chemtrail just keeps spreading out and forming a hazy cloud bank. These trails traverse the whole sky and stay for up to around five or even eight hours. They have been known to turn what was originally a clear blue sky into a grey haze.