The FAA has issued a new airworthiness directive for certain Cessna Aircraft twin-engine models after an investigation of recent and historical icing-related accidents. Aircraft covered by the AD, effective April 7, are certain Cessna models 310, 320, 340, 401, 402, 411, 414, and 421.
Specific aircraft affected are identified in Cessna Aircraft Co. Service Bulletin MEB97-4; the AD does not affect aircraft that are certified for flight into known icing conditions.
The AD was based on the FAA’s investigations of 51 icing-related accidents and incidents in the last 30 years. An unusual flight characteristic seen in the set of accidents and incidents the FAA studied was the development of high sink speeds that resulted in hard landings, suggesting the need for better airspeed awareness of pilots flying airplanes with accumulations of airframe ice.
According to the FAA, “These airplanes' certification basis did not include Amendment 7 of CAR 3 Dated May 15, 1956, which required an applicant to provide to the pilot the types of operations and meteorological conditions (e.g. icing conditions) to which the operation of the airplane is limited by the equipment installed (CAR 3 § 3.772). Therefore, the pilot may not realize that, even with de-ice boots or other similar equipment installed, the airplane is not certificated for flight into known icing conditions.”
Pilots can gain insight into the definition of "known icing" in a 2009 letter from the FAA that changes the agency's interpretation of the term from a rigid definition to one that incorporates pilots' decision making.
Under the AD, owners of the listed aircraft have two options to comply. They may incorporate the supplement provided in the AD into the airplane maintenance records and install a copy inside the airplane and accessible to the pilot during the airplane's operation. Alternatively, they can install a placard that indicates the aircraft is prohibited from flight into known icing conditions and install a placard that increases published airspeed on approach at least 17 mph (15 knots) when there is an inadvertent encounter with icing. Specific wording for the placards is also provided in the AD.
The actions required by the AD may be performed by the pilot or owner holding at least a private pilot certificate and must be entered into the airplane records showing compliance with the AD.
The FAA’s concern is that pilots/owners may not understand the certification basis of these aircraft and how it relates to ability to fly into known icing. The AOPA Foundation’s Air Safety Institute has resources on this topic, including: Weather Wise: Precipitation and Icing; Do the Right Thing: Decision Making for Pilots; and SkySpotter: Pireps Made Easy.