The National Transportation Safety Board determines that the probable cause of this accident was the flight crew’s failure to effectively monitor and maintain airspeed and comply with procedures for deice boot activation on the approach, which caused an aerodynamic stall from which they did not recover. Contributing to the accident was the Federal Aviation Administration’s failure to establish adequate certification requirements for flight into icing conditions, which led to the inadequate stall warning margin provided by the airplane’s stall warning system.

The safety issues discussed in this report include inadequate training on operations in icing conditions, inadequate deice boot system operational guidance, the need for automatic deice boot systems, inadequate certification requirements for flight into icing conditions, and inadequate stall warning margins in icing conditions. Safety recommendations concerning these issues are addressed to the Federal Aviation Administration.