Page:CAB Accident Report, Braniff Airways Flight 542.pdf/19

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through the engine structure canning gyrations of the rear of the engine within the confines of the adgacent shrouding and ducting Separation at the air inlet and compressor case Junction occurred in an upward and slightly to the left di— rection with the forward portion also rotating clockwise about a center five to Six inches outSide the bolt Circle peeitioned radially about the 11:00 o'clock postion This separation occurred by tenSion failures of the 1/4 - 28 cap crews and pullout of the 5/16 - 24 inserts. A study of this separation failed to reveal any eVidence of repetitive relativs motion as separation occurred. The loading necessary to bring about this separation could have occurred only after the QEC structural integrity was disrupted, and prepeller—generated loads that were intended to be absorbed by the Lord mounts which support the reduction gear assembly were instead transmitted rearward through the intact engine structure.

Interference of the first stage compressor blades with the air inlet houSing occurred on the No. 1 engine of this aircraft and on the Nos. 1 and 4 engines of the Electra involved in the acc1dent at Cannelton, Indiana. There was separation in flight of some portion of these three engines. These similar Circumstances cannot be accepted as coinCidental Since like circumstances prevailed in each case. It is believed this rotational interference was caused by air inlet case deflection due to abnormal loads being applied through the engine torquemeter housing and struts. Furthermore, these abnormal loads followed disruption of the engine supporting structure such that loads normally taken out by the forward QEC Lord mounts and structure were, instead, imposed on the engine structure. It follows that the baSic engine structure forward of the compressor must have been intact in order to trans— mit propeller generated case distorting loads The deSign strength of the baSic engine structure is materially greater than that required by the Civil Air Regula— tions for its supporting structure. This suggests that structural damage due to overloads by whatever means would be confined initially to the supporting structure. Thus, the preVious concluSion that engine supporting structure disruption preceded the engine structure damage is further substantiated.

No. l propeller blade angle and nmrklngs on the load 51GB of the compressor extenSion and stub shafts‘ splines indicate power was being produced when the separation occurred.

As stated under Investigation no indication of operational distress was found through examination of the hydraulic and electrical system components. Examination of the radio transmitters and receivers revealed no Sign of mal- functioning

Damage to the control surface boosters precluded establishment of booster selection, i.e.. "On" or "Off" or whether the autOpilot had been in operation prior to the breakup of the aircraft. Although the broken lead at the elevator load sensor probably failed as the result of a few (possibly three or four) cycles of reversed bending, it is not known whether the failure occurred prior to or as a result of the acc1dent. It may well have broken during the violent shaking which could have preceded the inflight breakup. If the failure existed in flight and the aircraft were being flown on autopilot the automatic eleVator trim feature would be inoperative and any change in longitudinal trim would be accommodated by the auto« pilot With the autopilot holding against an out—of—trnm condition, up to the limit of its authority, sudden release of the autopilot would result in a rela- tiVely mild pitchup or pitchdown, depending upon the direction oftrim imbalance.