The FAA is reissuing and revising a Special Airworthiness Information Bulletin (SW-08-03R4) covering recommendations for rotorcraft powered by turboshaft engines flying into snowy or icy conditions. The SAIB describes procedures to reduce the probability of an uncommanded in-flight engine shutdown due to snow and/or ice ingestion and reminds operators that most helicopters are not approved/equipped for flight into icing conditions.
The FAA notes that the condition remains an ongoing safety concern. “We are revising and reissuing this SAIB because ice and snow ingestion continue to be a contributing factor in helicopter accidents. During the winter months of early 2013 at least two helicopter accidents were suspected to have ice or snow ingestion that led to loss of engine power. One of these accidents resulted in fatalities. In several instances aircraft were sitting outside during periods of rain, sleet or snow with below-freezing temperatures for a period of time before the accident flight. Some of the aircraft even ran several minutes on the ground before takeoff before their engine lost power in flight due to suspected ice or snow ingestion.”
During ground operations, the FAA notes that “snow and ice can build up in the engine intakes and plenums when the rotorcraft is on the ground with the engine(s) not operating or are operating at a low power setting for extended periods.” When engine power is applied, these buildups can be ingested, resulting in decreased power or engine failure. The FAA notes that the problem is more acute on aircraft with early turboshaft engines featuring axial inlets.
Response to Icing Conditions
The FAA cautions that icing can occur whenever there is visible moisture and the temperature is below degrees 41 degrees F (5 degrees C) and that pilots need to have an escape plan to get to warmer air.
It recommends the following additional actions:
• Never operate in snow or icing conditions if prohibited by the rotorcraft flight manual (RFM).
• Never operate in snow or freezing conditions without the snow protection kit for the engine inlet if one is provided by the manufacturer.
• Land as soon as possible after hovering in snow or icing with unprotected inlets, shut down the engines and inspect the inlets for ice and snow unless another procedure is spelled out in the RFM.
• Beware of visual signs and flight indications of ice accumulation such as ice on antennas and degraded rotor performance.
• Perform a thorough preflight that includes current and future weather information from the local FSS, the icing tool (weather.aero/icing) and the HEMS flight tool (weather.aero/hems).
• Use aircraft inlet and exhaust covers whenever the aircraft is parked outside and move aircraft to a covered area, when possible, or otherwise protect the aircraft whenever snow or ice is anticipated.
• Perform a complete inlet/exhaust inspection with a flashlight before engine start, and including surfaces inside and around the inlet and behind the particle separator screen.
• Remove all snow and ice using heated air or de-icing fluid, not by chipping and scraping, paying particular attention to sheet ice on the bottom or forward of the inlet. This may require opening the cowling. Use engine preheating if required.