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ANALYSIS OF EVIDENCE
The results of the examination of the wreckage pointed quite definitely to a failure in the air of one or more elements of the airplane's structure. The condition to the left wing indicated that a failure of the tip occurred prior to the impact of the airplane with the ground. This conclusion was reached on the basis of a number of significant clues. Firstly, the break along the wing chord, evidenced by predominantly tensile failure in the bottom skin, indicated bending of the tip in the upward direction. It is highly improbable that such a mode of failure would have resulted from impact when the inertia of the wing tip would tend to produce downward forces. Secondly, there were absolutely no signs of the tip's contact with the ground. Although the soil at the scene of the accident was very light in texture and free from stones, it seems inconceivable that the wing tip could have struck the ground without suffering some scratches from contact, or without leaving particles of soil at some of the numerous rivet-heads, edges of overlapped skin, etc. Finally, the very obvious pattern of oil spots on the wing is significant. These oil spots apparently were the result of damage to the engine lubricating system incurred at the time of impact. Their location along the span of the left wing indicates that almost instantly after impact the tip was in a folded position on top of the wing. Additional clues found in the examination of the wreckage also supported the contention that failure of the left wing tip did occur in the air.
No signs were found which would point to any additional failures of the wings in the air, except perhaps that of the right wing tip. Since this wing hit the ground more violently, and the tip sustained appreciable damage from contact with the ground, it was difficult to ascertain its condition prior to impact. However, the fact that it was found detached from the remaining portion of the wing panel and has rolled over a few times after the original impact is regarded as significant. Had the wing tip been intact before hitting the ground it is improbable that it would have sustained damage of the type actually incurred by contact with the ground. It is entirely possible therefore that the right wing tip also failed in the air, although there is less evidence to that effect than exists for the failure of the left wing tip.
A study of the conditions of the tail surfaces, as found after the accident, led to the belief that the horizontal surfaces also had failed in flight. Although the evidence in this respect was not quite so conclusive as in the case of the left wing tip, nevertheless it was sufficient to warrant further study. In view of the somewhat unusual, multiple fractures in the right elevator, parts of this assembly were submitted by the Board to the Division of Metallurgy at the National Bureau of Standards. The Bureau's findings confirm the conclusion that the right elevator had failed prior to impact with the ground, indicating further that the failures were the result of excessive air loads imposed on the structure, and that no signs of fatigue were noticed in the examined parts. The Bureau of Standards' conclusion that the right elevator had failed in flight was based on the fact that both up and down forces of appreciable magnitude had acted successively on the elevator. The forces in the up direction deflected the elevator torque tube, broken in two places, through a total angle of over 90°, which would not be expected to happen if the forces were due to impact of the structures with the ground.
- "Air loads" are the external forces imposed upon the airplane by reason of its movement through the air.