Cessna 441 N779CC accident near Fargo, North Dakota

Probable cause

The pilot’s failure to cycle the surface deice boots during the instrument approach in icing conditions, which led to ice accumulation on the leading edges of the wings and empennage, and resulted in an aerodynamic stall and subsequent hard landing.

NTSB analysis

The airline transport pilot reported that the accident flight was the airplane's first flight after a phase maintenance check, and that he was repositioning the airplane to an airport about 40 nautical miles away. While en route, the airplane experienced a series of avionics and fuel-related anomalies. The pilot eventually declared an emergency and was cleared to land at the destination airport. The first approach for landing in instrument meteorological conditions resulted in a missed approach. The pilot reported that, about this time, the airframe was accumulating ice and he cycled the deice boots.

During the second approach, the airplane broke out of the clouds, and the pilot proceeded to land. The pilot reported that, before he initiated the landing flare, he reduced engine power to idle, fully extended the flaps, and flared the airplane. He stated the airplane was shaking and shuddering, but no stall warning horn sounded, and then the "bottom fell out." The airplane landed hard, and the left engine's propeller blades struck the runway. The airplane incurred wing spar and propeller damage.

A postflight examination of the airplane revealed between ½ to 1 inch of rime ice on the leading edge surfaces of both wings, the horizontal stabilizer, and the vertical stabilizer. The pilot's operating handbook for the airplane stated that the deicing boots should be cycled as necessary when ice accumulation reached between ¼ and ½ inch. The amount of ice on the wing and empennage surfaces after the accident was consistent with the pilot not cycling the deice boots as prescribed, which resulted in an excessive ice accumulation on approach and a subsequent aerodynamic stall during the landing flare.

Text from the NTSB. Open the NTSB docket for CEN16LA098 for the full record.