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operating from the only Navy facility in the area and further that no other Naval command had aircraft operating in the vicinity of Buffalo. The Air Force reported no local flights from Barksdale Air Force Base between the hours of 2200 and 2.40%. Connelly Air Force Base had aircraft in the area, but all had landed prior to the time of the acc1dent. Carswell Air Force Base had two KC-135's on IFR round robins at accident time. (If these two had been in the Buffalo area IFR, ARTE} should have had a record of this.)
5. In all of the examination, testing, and analysis of the flight control systems, boost, and autopilot, no phenomenon could be produced which would pro- duce or lead to a structural failure. (There was further work done in this area after the Cannelton accident.)
There is one other very important conSideration. This is the Cannelton, Indiana, accident of a Similar Electra, which also experienced a wing failure (right) and loss of QEC units to form a Similar destruction pattern of the Buffalo accident. While a mirror image type of pattern itself is not pOSitive proof of Similarity of cause, there are indications of oscillatory motions of wing and out— board QEC structure in both the Buffalo and Cannelton wreckages.
Followmg the accident at Cannelton, Indiana, Lockheed undertook a reevalu- ation program in which the entire Electra concept and decign was audited. An enormous quantity of data was produced, the maJority of which was negative. It is sufficient for the purpose of this report to state that, insofar as causal factor is concerned, only one area of the program is significant. This is the phenomenon known as "whirl mode," an oscillation which under Certain conditions can produce flutter.
All of the flutter tests and analyses made by Lockheed during the original certification process and during reevaluation showed the Electra to be flutter— free during and even above normal operating speeds and further disclosed that the wing has a high degree of damping. The term "damping" means that if a motion is imparted to the structure, the motion will die out when the exc1ting force is re— moved; the damping forces are those which take energy away from the OScillation. A small amount of damping is from internal energy absorption in the structure and in energy absorbers such as engine mounts. The most Significant damping, however, is the result of aerodynamic forces acting in OppOSition, thus absorbing energy from the oscillation Conversely, if a major change occurs that allows the aero- dynamic forces to be additive to the exciting force, the oscillation grows, and the result is flutter
Since the Electra Wing is baSically flutter resistant, in order to produce flutter there must be an external drivmg force. The poss1ble force generators are the control surfaces and the propellers. Analyses indicated that the control surfaces would not produce wing osCillations of sufficient amplitude to produce a wing failure; consequently, further analysis was centered around the propeller.
The propellers being normally stabilising, it was necessary to consider abnoml prepeller behaVior, such as overspeeding and wobbling. The studies and tests conducted during the reevaluation program proved that a wobbling outboard propeller caused by weakened nacelle and/or engine structure can induce wing oscillations.
