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momentary interruption of oil could be caused by the negative acceleration which would create a movement of oil away from the oil outlets in the tank, exposing the outlets to air. That such a condition is possible is borne out by the testimony of witnesses during the hearing.
This negative acceleration could be caused by a sudden dive or by having the airplane go over on its back or by a severe down gust. It is not likely that interruption to the oil supply during stable flight conditions could cause over-revving since if the oil interruption had occurred while these conditions obtained, the rate of rotation of the blades to low pitch would be at the slow rate of approximately one degree in eleven seconds.
Under normal conditions the propeller blades would have rotated toward the high pitch stop (about 45 degrees) while the airplane was accelerating and descending at high speed. From the fact that the pitch angle at time of impact appeared to be 24 degrees, which is a cruising angle, it may be inferred that the interruption in oil supply which might have taken place and which would tend to rotate the blades to low pitch, balanced the tendency of the blades to go into high pitch as a result of the high speed of the airplane. Under such conditions the propeller would have the characteristic of a fixed pitch propeller. If the propellers had been windmilling at a pitch setting of 24 degrees and at 3000 RPM, an airplane speed of 320 miles per hour would be indicated. If the propeller had been windmilling at 24 degrees and maximum engine RPM of 2350, it is estimated that the airplane speed would have been about 250 miles per hour.
