Page:CAB Accident Report, TWA Flight 891.pdf/52

 -52- 1. Wing flutter

The data mentioned in par. 11.3.6 show that the Wing is free from self—induced vibration up to the speed of l. 2 V9 (391 knots) and under any condition of fuel load.

Since the worst condition exists when the wing has a fuel load of 7,650 gallons, it follows that With the fuel load the plane was carrying at the time of the accident (2,200 gallons) the pQSSibility of flutter was very remote. BeSides, the flutter would have caused

the manmum bending stresses in the area of the nacelles of the outer engine and the maxim torsion stresses

in the area between the outer and inner nacelles. Examination of the structural parts recovered revealed no breakage from stresses of this type. Lastly, it is to be conSidered that self-induced flutter Vibrations would very likely have caused the lead masses fitted

on the leading edges of both Wlng tips to break away during flight. Instead, they were recovered very

close to their respective Wing portions. All this shows that Wing flutter could not have been a determining cause of the accident.

2. Tail flutter

As in the case of the wing, the absence of flutter up to the speed of l, 2 V = 391 knots EAS was ascertained also with respect to tRe tail assembly. Furthermore, the traces of smoke and fire on the tail assembly show that the separation of the tail took place after the events which caused the acCident (see par. 11.2.3.”

Therefore, as "in the case of the wing, tail flutter cannot be conSidered a primary cause of the accident.

lh.h.1.11 Breakdown from excesSive rolling or excesSive yawing

L'onclus ion:

A Violent rolling maneuver, or an excesswe rolling speed, would have caused signs ofttorSion on the Wing covering in the area of the outer nacelles - which signs were not found — or aileron breakages of a type different from those observed when the wreckage was exammed. With respect to yawing maneuvers, the most critical structures are the back portion of the

fuselage and the vertical tail surface. Actually, there is evidence that the plane was yawing at a high angle of drift, with strong side stresses, but the traces of fire on the tail aSSembly and the symmetrical nature of the breakage on the tail indicate a breakdown from exceSs of unsymmetrical loads

while yawing as the primary cause of the accident.

0n the basis of the premise stated above, namely, that before the crash the plane was in normal condition as regards care