Page:CAB Accident Report, Pennsylvania Central Airlines Flight 19.pdf/47

 angle is that it fails to provide the negative acceleration of the airplane which would be a possible explanation of the apparent over-speeding of the propellers. A negative acceleration suggests inverted flight, and consideration has been given to the possibility that the flight path might have had the form of an S, the airplane having been on its back at a midpoint of the descent, and a recovery from that attitude having then been started but not completed before striking the ground. Such a path would be possible in the event of a temporary disabling of the pilots or a temporary interference with the control, a difficulty lasting only a few seconds and followed by resumption of control of the airplane. It would account for the negative acceleration, and consequent over-revving of the propellers. It would account also for the fact that several of the witnesses living near the scene of the accident spoke of the roaring noise that immediately preceded the crash as having seemed to come from the west, over towards the mountain,—for if the airplane had actually taken the shaped path downward, its first deviation from its normal attitude would have occurred when it was approximately over the point of final contact with the ground, and therefore well into the rainstorm area.

Another alternative is that the airplane might have spun from a considerable altitude, or descended on an irregular path after the wing had stalled. The reasons for discarding those hypotheses are explained elsewhere. In addition to the reasons given there it would appear that there could not have been any large amount of side-slipping or turning on the way