Page:CAB Accident Report, Braniff Airways Flight 542.pdf/18

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prior to extinguishment, a smaller fire emerged from the large ball and fell to the northeast, dying out well before reaching ground level.

That the aircraft broke up Violently is self-eVident. That the breakup process was both quick and with little or no warning is also clear for two reasons. First, only one of the 37 aircraft's passanger seats recognizable as such was found with the safety belt fastened, and this probably means there was no time to order their fastening. Second, the final radio message preceded the breakup by an interval of something less than two minutes and that message gave no hint of trouble.

A definite sequence of failures and breakages appears discernible and will be mentioned because it may be conSidered as somewhat baSlC for this analySis. Sep— aration of the left wing and the No. 1 gear box propeller and QED structure occurred at about the same time, it is impOSSible to say which went first. The horizontal stabilizer then broke up under the impact of parts coming from the wing; wing planking from the right wing tip came free; the No. 4 powerplant tore loose; and the right wing outboard of No. 4 separated. All of these events happened in a short period of time. Somewhat later, at much lower altitudes, the fuselage broke in two separate portions at a point about halfway back near fuselage station No. 5T0.

Under Powegplants mention was made of there being no ev1dence of overspeeding. However, in View of the tolerance of both the engine and propeller to overspeedlng before any physical eVidence develoPS, 20 percent and 53 percent, respectively, lack of this eVidence does not permit concluding an overspeed of a lesser amount did not occur. However, it is difficult to progect an overspeed as such into an accident of this kind, The following devices are incorporated in the engine pro- peller deSign to protect against overSpeeding and/or high drag: (1) fuel control overspeed governor, (2) negative torque Signal, (3) safety coupling, (4) hydraulic and mechanical low pitch stops, (5) beta followup, and (6) pitch lock. These features, some of which function entirely independently, pr0V1de multiple protec- tion against powerplant induced drag of a degree which would present airplane control or structural loading problems.

Also, under Powegplants there is mention of pOSSlble emergency procedures having been used on No. 3 powerplant. However, the eVidence indicating that emergency action may have been taken with reSpect to No. 3 powerplant is not sup— ported by the phySical condition of the engine and propeller. This powerplant was the last to separate from the airplane, possibly at contact with the ground. That the Oil shutoff valve was only partially closed indicates the Operation was prematurely ternnnated, most likely by a loss of electrical power. It appears that emergency action with reapect to this engine was initiated Just prior to or during breakup by either the crew of by actuation of the control due to disruption by the airplane breakup. Any significance of these valves with respect to the accident is not discernible.

In reference to the statement under Powegplants that the No. l propeller, engine gear case, torquemeter, air inlet case, and QEC structure separated and fell as a unit, the following should be noted. This separation occurred following failures in the QEC which permitted movement of the rear of the engine. Had the engine separation occurred first the repeated markings made on the adgacent shroud— ing by the clamp on the rear of the engine would not have occurred. It is concluded that the normal support provided by the mounts at the reduction gear case was dis— ruPted, thus permitting loads generated.by the rotating propeller to be transmitted