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Turbulence
The Board has given consideration to the possibility that the accident may have resulted from turbulence so violent as to throw the airplane out of control.
Flying through turbulent air is not, of course, an unfamiliar experience for any transport pilot. It customarily involves nothing more than abrupt accelerations of the airplane, with resulting discomfort for the passengers, and an increased need for alertness on the pilot's part to keep the airplane on its course and to restore it to a normal attitude after any particularly violent disturbance. Instances are known, however, of airplanes having encountered turbulence of such extraordinary intensity as to momentarily throw them completely out of the pilot's control and into wholly abnormal attitudes. Cases have been reported of airplanes having encountered gusts so violent as to stall[1] the wing completely, from a flight speed considerably above the normal stalling speed. Stalling due to turbulence, without there having been any ice on the wings to increase the susceptibility to such stalling, is extremely rare, but cannot be absolutely eliminated as a possibility.
When an airplane of the type involved in the Lovettsville accident is deliberately stalled with power on, the stall customarily develops first on one wing-tip and that wing drops sharply, the airplane simultaneously turning toward the low wing. Where the maneuver is deliberately executed by a pilot who is prepared to initiate immediately the required measures of recovery, evidence received in the present investigation indicates that only
- ↑ Stall. A wing is said to be stalled when the angle at which it is moving through the air becomes so large (usually as a result of attempts to reduce the speed too far, or climb too steeply) that the air no longer flows smoothly along the upper surfaces of the wing, but eddies irregularly, resulting in sudden changes of lift and great instability.
