Cessna 208B N207DR accident near Kwigillingok, Alaska

Probable cause

The pilot's decision to take off with ice-contaminated wings in freezing rain and mist, which resulted in an aerodynamic stall.

NTSB analysis

Passengers reported that prior to departing on the accident flight they observed ice on the wings and described the weather as foggy, with freezing rain. Shortly after takeoff, at an estimated 200 feet above the ground, the pilot reported a series of power fluctuations, coinciding with a loss of altitude. The pilot stated that he engaged the emergency power lever, and that power was restored, but not before the airplane collided with a frozen lake, damaging the right wing. The airplane subsequently became airborne, and the pilot elected to fly to another village to land.

A postaccident inspection disclosed no mechanical anomalies with the engine or its accessories, and the airplane was flown to its base after the wing was repaired without any engine problems noted. A weather study by a Safety Board meteorologist determined that the area was subject to light snow showers, freezing fog and mist, and surface temperatures below freezing, all conducive to wing/airframe icing. During an interview with Federal Aviation Administration inspectors, the pilot acknowledged seeing “a trace of ice” on the wings. The limitations section of the airplane's flight manual supplement "Known Icing Equipment," states, in part: "Takeoff is prohibited with any frost, ice, snow, or slush adhering to the wings, horizontal stabilizer, vertical stabilizer, control surfaces, proper blades, or engine inlets." The limitations section also includes the following: "WARNING, EVEN SMALL AMOUNTS OF FROST, ICE, SNOW OR SLUSH ON THE WING MAY ADVERSELY CHANGE LIFT AND DRAG. FAILURE TO REMOVE THESE CONTAMINANTS WILL DEGRADE AIRPLANE PERFORMANCE AND MAY PREVENT A SAFE TAKEOFF AND CLIMBOUT."

Text from the NTSB. Open the NTSB docket for ANC10LA019 for the full record.