Page:CAB Aircraft Accident Report, Allegheny Airlines Flight 371.pdf/9

- 9 - It is believed that the fluxgate compass was functioning as evidenced by the fact that the captain had successfully completed an instrument approach and subsequent examination of the fluxgate showed it to be operable after the accident.

The position of the caging switch on the back of the pedestal (see Attachment "B") coupled with the lack of a guard for this switch left it exposed to accidental actuation by any person occupying the jump seat.

Analysis of the fact situation revealed by this investigation indicates that the caging switch could have been accidentally actuated by the foot of the crew member occupying the jump seat during the initial part of the base leg. This is considered likely since at this segment of the approach the crew members would be attempting to locate the landing runway and it is probable that the crew member in the jump seat would have been leaning forward in an effort to locate the runway and would thus have made some contact with the rear of the pedestal because of its proximity to the jump seat.

Accidental caging of the fluxgate compass with the aircraft on any southeast or southwesterly heading would have induced an error to the right which would have shown up on the MDI by indicating the aircraft was turned to the right in excess of its actual heading.

It is believed that the captain was induced to refer to his instruments on the base leg of the landing approach because of the restrictions to visibility encountered and by cockpit limitations to his field of vision. The captain continued his turn intending to roll out on the runway heading but reference to the MDI indicated that he had overshot his heading so he immediately turned to the left to an indicated heading of 270 degrees. After rolling out on this heading he was unable to see the field which was now to his right and he continued on for a few seconds expecting to see the field momentarily. Owing to the induced error of approximately 80 degrees to the right the aircraft was now on an actual heading of approximately 190 degrees and the heading for Bald Eagle Mountain. The aircraft then encountered solid instrument conditions. The captain continued his flight on the indicated heading of 270 degrees for approximately 12 to 14 seconds, during which the aircraft was converging with the northern slope of Bald Eagle Mountain. During this time the captain noted the discrepancy between the MDI and his other directional instruments and caged the fluxgate compass in an effort to determine his correct heading. Upon completion of the caging cycle the MDI turned to a heading of approximately 190 degrees. At this time, just prior to the crash, the aircraft was turned to the right, full throttle was applied, and gear retraction was initiated. Before this turn could be completed the aircraft crashed into the trees and rocky terrain of the mountain.

The possibility of accounting for the left turn by the captain having initiated an abandoned approach was also considered. For this to have occurred the induced error in the fluxgate compass would have to be to the left in the order of 80 degrees and would have been induced by accidental caging of the fluxgate compass while on a northeasterly or northwesterly heading. With such an error and if the captain turned to an approximate heading of 100 degrees to go back to the L/F range, the aircraft would then have been on an actual heading of 180 degrees. This is compatible with the statements of the ground witnesses.

Several facts indicate that this possibility did not occur. The aircraft struck the mountain at approximately the same altitude that it was seen when departing the