Airworthiness Directives; Cessna Aircraft Company Airplanes

We are adopting a new airworthiness directive (AD) for certain Cessna Aircraft Company (Cessna) Models 310, 320, 340, 401, 402, 411, 414, and 421 airplanes. This AD was prompted by an investigation of recent and historical icing-related accidents and incidents for the products listed above. This AD requires either having the supplemental airplane flight manual/airplane flight manual supplement (SAFM/AFMS) inside the airplane and accessible to the pilot during the airplane's operation or installing a placard that prohibits flight into known icing conditions and installing a placard that increases published airspeed on approach at least 17 mph (15 knots) in case of an inadvertent encounter with icing. We are issuing this AD to correct the unsafe condition on these products.