Page:CAB Accident Report, United Airlines Flight 21.pdf/79

 The stalling speed of the aircraft was raised an undetermined amount by the ice accumulation on the leading edges of the wings.

Captain Scott failed under the conditions set forth above to maintain adequate flying speed.

Upon the basis of the foregoing findings of fact and upon all the evidence available at this time, we find that the probable cause of the accident to aircraft NC 25678 (United 21) on December 4, 1940, was the failure of the pilot to exercise that degree of caution and skill required to avert a stall while approaching for a landing on the short northwest runway. A substantial contributing factor to the accident was the error in judgment of Captain Scott in choosing that short runway for his landing.

An adequate stall-warning device has been recognized as much needed in connection with air carrier services and other aircraft operations for a long time. Some research has been conducted along this line, but to date nothing has been developed which appears to be reliable under all conditions, particularly under icing conditions. The Board recommends that the Administrator of Civil Aeronautics give this matter the utmost encouragement through appropriate channels, including the aviation industry, in an effort to accelerate the further development of an adequate stall-warning device. The Board also recommends the continuance of research into the more functional problem of developing wing surfaces which are not subject to critical behavior at or near the stalling speed. 