A recent aviation disaster in Vinhedo, Brazil saw a commercial plane crash in a residential area, resulting in the tragic deaths of all 62 people on board. The possible cause of the crash was attributed to icing on the wings, raising concerns about the threat of aircraft icing to flight safety. How should pilots deal with this issue?
According to aviation news website Simple Flying, aircraft icing refers to the accumulation of ice on the surface of the aircraft. This can lead to performance degradation, increased fuel consumption, and in the worst-case scenario, loss of control and a crash. Therefore, anti-icing and de-icing systems are crucial components for the safe operation of an aircraft.
Airframe icing is caused by supercooled water droplets, which can maintain a liquid state at very low temperatures due to the lack of freezing nuclei.
When pure water droplets are cooled to extremely low temperatures or encounter freezing nuclei, they turn into ice. Freezing nuclei can be a speck of dust or any other form of impurity, causing water to freeze around it.
Supercooled water droplets can exist within the temperature range of 0 to -40 degrees Celsius. There are many supercooled water droplets between 0 and -20 degrees, posing significant challenges to aircraft. Supercooled water droplets between -20 and -40 degrees are rare.
When the temperature drops below -40 degrees, supercooled water droplets cannot remain in a liquid state and will freeze, causing aircraft icing only when the temperature suddenly plunges to below -40 degrees Celsius.
When the leading edge of the wing ice up, it disrupts the smooth airflow needed for the aircraft to generate lift. This leads to loss of lift and increased drag, making the aircraft’s performance inefficient. It also increases the risk of stalling by reducing the angle of attack.
In aircraft equipped with conventional non-powered flight control devices, ice may form between aerodynamic balancing devices (such as control horns), potentially blocking the control surfaces. Ice buildup also adds weight to the aircraft, increasing both fuel consumption and overall drag.
Aircraft icing can also pose a danger to the engines. Icing typically occurs at the engine inlets, which can detach and possibly enter the engine. These ice fragments may impact the fan blades of the engine, causing significant damage. Blade damage can also disrupt airflow within the engine, leading to a stall.
Furthermore, when droplets ice up as they fall from the fuselage, they create ice ridges. Ice ridges forming near aircraft sensors (such as pitot tubes) can interrupt airflow, leading to erroneous data readings by the sensors.
Ice comes in several forms, including clear ice, rime ice, mixed ice, freezing rain, and hoar frost, with clear ice posing the greatest danger to aircraft.
Clear ice is formed when supercooled water droplets strike the aircraft. As heat is released during ice formation, it slows down the freezing process, causing some droplets to flow back onto the surface and freeze. Clear ice tends to cover a large area of the aircraft, and because it is transparent, it can be difficult to detect once formed, increasing weight and causing balance and control issues.
Aircraft icing conditions can be categorized into four types:
– Trace icing: When icing becomes visibly noticeable, it is known as trace icing. At this point, the ice accumulation rate is typically higher than the sublimation (ice vaporization) rate. This type of icing is not very dangerous unless prolonged and can be managed without de-icing and anti-icing systems.
– Light icing: In cases of light icing, prolonged flight for over an hour can lead to ice accumulation issues. The use of de-icing and anti-icing systems can easily remove light icing or prevent its formation.
– Moderate icing: Moderate icing, even in a short period, can be hazardous. Pilots may need to alter the aircraft’s altitude, course, and continue to use de-icing and anti-icing systems.
– Severe icing: When de-icing and anti-icing systems fail to reduce ice accumulation, it is considered severe icing. Pilots must immediately get the aircraft out of icing conditions without delay to ensure flight safety.