Less than two months after two possible weather-related fatal crashes of EMS helicopters in Illinois and Iowa, the FAA issued a Special Airworthiness Information Bulletin (SW-08-03R3) 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 recommends that pilots abide by their rotorcraft flight manual regarding flight into these conditions; conduct a thorough preflight weather evaluation; install engine inlet and exhaust inserts/covers whenever an aircraft is on the ground with engines not operating; refrain from prolonged engine idling/running while on the ground; thoroughly inspect inlets for ice/snow prior to takeoff; and remove any discovered ice/snow from inlets with either de-icing fluid or heated air, not by chipping or scraping.
The FAA notes, “In freezing temperatures, pay particular attention to sheet ice on the bottom and forward of the inlet. This ice can also form behind particle separators. Engine preheating may be required.”
In-flight indications of icing include visual cues, such as “ice accumulation on mirrors, wipers and antennas. Pilots should also be mindful of possible increased vibrations or power requirements. The degraded performance of the helicopter may be due to increased weight and possible degraded rotor performance due to accreting ice.”
Pilots need to be aware of conditions that promote ice formation, including visible moisture and temperatures below 5 degrees C (41 degrees F). “Pilots should be aware that icing is possible in these ambient conditions and should be prepared to leave the area of visible moisture or change to a warmer altitude as soon as possible. (Note: This ‘warmer’ altitude may not always be a lower altitude.)”
The SAIB includes links to resources such as NASA’s Icing Tool, the helicopter emergency medical systems flight tool and Transport Canada’s Aviation Safety Letter article about helicopter operation in icing.