Icing on Airplanes
Frost conditions can be expected when the air temperature drops below the freezing point when the humidity turns into a form of precipitation or becomes dense. This can be precipitation, rain, sleet, or snow. It can also occur as a result of icing, condensation, or fog.
Cases of icing usually occur in harsh weather conditions. However, even if the outdoor temperature is above the freezing point, if the air surface is below the freezing point and there is moisture in the air, frosting may occur.
When the drizzle falls on the plane surface below 0 ° C, a transparent ice layer is formed on the wings. In the performance of the aircraft, unpolluted and clean airplane surfaces are very important.
Collecting ice, frost, and snow on the plane surface increases the weight of the plane, and plays an important role in the aeration of the plane and in the pulling forces. Otherwise, a safe flight is not possible. In short, there should never be ice, snow, frost, and slush (incompletely melted ice or snow) on the surfaces of an airplane ready to fly.
Sometimes a transparent and invisible ice layer may form on the upper surfaces of the aircraft wings. This situation may also cause icing on the lower surfaces of the wings. This type of icing is called transparent icing. While the wings are moist, it is quite difficult to detect clear ice in poor light during checks. It is quite difficult to notice the transparent ice from the cabin. Because the transparent ice is transparent, the details of the wing surface are visible from the outside of the ice. Transparent ice formed on the upper surface of the wings is very dangerous for aircraft with rear-linked engines. When the plane is taking off or landing, the ice that is adhered to the wing surface is broken and leaves the wing due to the flexibility formed on the wings. These separated ice sheet fractures are absorbed by the motors and damage may occur depending on the size of the ice.
Factors that play a role in the formation and thickness of the transparent ice sheet
The fuel added at the previous stopping of the aircraft is at low temperature or at the end of the long flight time before, the temperature of the fuel remaining in the tank is below 0 ° C.
Due to the considerable amount of cold fuel levels in the wing tanks, the wings will touch the upper surfaces (around the wing fuel tank)
The warm fuel added during the stopping of the aircraft melts the falling snow and this melted snow freezes again.
Thin rain droplets and ambient temperatures of 0 ° C are quite effective in icing cases. It was reported that heavy freezing events were reported even at 8-14 C during thin rain.
In the use of a thermal icebreaker at the edge of the attack, when the snow falls on the surface, it may melt and freeze again.
Most Freezing Sensitive Areas
Wing bottoms between the front and back spars.
Any part of the wing containing unused fuel after the flight.
Where the wing has different structures (cold metal parts) such as the areas above the spars and the main landing crew.
The best control of the wing top surface is about to be touched by going up a ladder placed close to the body as well as being able to touch it. This is especially important for the part where the fuel tank is located. If transparent ice appears in the response of the control, it should be tested again whether the flap has been completely cleaned after cleaning. Frost may occur on the surface due to precipitation when the plane is landing. If the temperature is low in the areas where the plane is flying, ice collection may be invisible to the moving and fixed places when the flaps are pulled. Therefore, regardless of the aircraft's take-off, these parts should be controlled. In the case of freezing fog conditions, it is necessary to check whether there is icing on the propellers first. If an icing decision is observed, affected areas should be defrosted provided that they benefit from low-flow hot air sources.
Anti-Icing and De-Icing System
While the aircraft is in the air, the wings and motors are prevented from freezing from the engines by hot air or electric heaters. However, these systems cannot be used to clean or defrost snow or ice collected on wing and tail surfaces while the aircraft is on the ground. For this reason, defrosting / anti-icing operations carried out with the aircraft on the ground are works to remove the sensitive (wing and tail) surfaces of the aircraft from any icing or snow accumulation. Defrosting (Defrosting Process): It is the process created to clean ice, frost, snow, and slush (not melted snow) in the plane. In this process, hot water or a mixture of hot water and de-icing fluid is applied to the outer surface of the aircraft.
Anti-Frost (Ice Prevention Process): It is the operation (holding time = protection time) to prevent the accumulation and sticking of snow, frost, and ice for a certain period of time on the plane. In this process, anti-icing fluid, water mixture, or anti-icing fluid is applied to the aircraft.
The responsible captain decides whether the aircraft will take de-icing or not according to the determined rules and conditions. This location is provided to the passengers to be informed and announced. De-icing / Anti-icing takes about 10 minutes after the plane takes the passengers and closes the door. During this period, the operation of the ventilation system is restricted so that the passengers are not disturbed by the smell of de-icing / anti-icing fluids.
In this case, it is applied by deciding the “DE-ICING and ANTI-ICING” process with the aviation expression, which can also be called alcoholization in the public. DE-ICING is to remove the existing pollution (snow-ice) from the aircraft, and ANTI-ICING is to protect the aircraft by being covered with a liquid for a certain period of time (until it leaves the take-off and icing conditions). If the plane does not have any contamination (snow and ice accumulation) on the ground, de-icing is not required most of the time. Only anti-icing is sufficient.