Page:CAB Accident Report, Pennsylvania Central Airlines Flight 19.pdf/66

 even argues against the possibility of a stall having taken place after the airplane had for some reason descended to low altitude, since the dropping of a wing in the stall is attended by a considerable turning of the airplane and recovery from the stall is not normally on the same heading on which the maneuver was started. The same reasoning applies, with even more force, to any theory that the airplane might have stalled in conditions of such violent and continuous air turbulence that the pilots were never able to regain control during the 20 seconds or more that would have ensued before the machine would have struck the ground. The presumption of turbulence of that order, and continued over so long a period, seems in any event a virtually incredible one in the light of all that is known of atmospheric structure. It would, in any event, have been impossible for violent turbulence to extend to a very low altitude without having shown itself as a surface wind.

A possibility that may be considered in connection with the discussion of turbulence, though it is not strictly in that category, is the action of a simple down-draft or descending current of air. Thunderstorms are characterized by violent vertical motions of the air, and especially by rising currents, often of very high velocity. Such rising currents have been known to attain a velocity of several thousand feet a minute. In undisturbed air, at 6000 feet, the maximum rate of climb of a fully loaded aircraft of the type involved in this accident is approximately 600 feet per minute at take-off power. Even with one engine dead, the maximum rate of climb would be over 100 feet per minute. If the airplane had flown out of a rising current in front of the storm and directly into rapidly descending air, approximately as it entered the rain, it is conceivable that it might have been impossible, even with the application of full power, for the pilot to avoid a rapid loss