Ice as a Challenge to Engine Protection
Flight in icing conditions is a significant and a known hazard for all aircraft. The accretion of ice on an aircraft is caused by super-cooled water droplets impacting the aircraft’s surfaces and freezing.
Icing is among aviation's most serious weather hazards because it can severely reduce an aircraft’s performance during flight. Icing mostly occurs at lower altitudes, impacting small fixed wing aircraft and helicopters that fly slow and low. Icing causes mission delays during ground de-icing of aircraft, mission cancellations, and abortions because of forecast or actual in-flight icing.
Icing can take place on any exposed part of the aircraft and can generate several different types of hazards. For rotorcraft, these hazards can include: degradation of the aerodynamic performance of rotors, fouling of sensors and external moving parts, increased mass due to accreted ice, increased vibration (due to increased mass, shedding or changes in the aerodynamic profile of the rotor blades), reduced visibility through the windscreen and other windows, damage caused by shed ice, changes or reduction in air intake flow, ingestion of shed ice or slush.
The regulations state that, if a flight is to be made into known or forecast moderate icing conditions, the aircraft must be equipped with adequate de-icing or anti-icing equipment. The restrictions are stated in the operator's manual for each aircraft (See latest FAA recommendations
). “When a plane flies through super-cooled water droplets, ice accretion occurs on the air intakes. The ice deposit can cause aerodynamic airfoil degradation, or engine flame outs due to ice ingestion coming from the air intakes” (ONERA, French Aerospace Laboratory).
Snow Regulations for Helicopter Engines
“It must be shown that each turbine engine and its air inlet system can operate throughout the flight power range of the engine (including idling), in snow, both falling and blowing, without adverse effect on engine operation, within the limitations established for the rotorcraft” (ref JAR/FAR-27/29.1093). See latest FAA recommendations