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flight did not experience any turbulence, and one of the previous flights described light to moderate turbulence, the latter flight maintained a rough air penetration speed. Additionally the flight recorder readout from this flight revealed acceleration excursions up to 1.0-g which is the upper limit of the moderate turbulence range. Accordingly the Board concludes that N804L Was in an area of at least moderate turbulence.
Despite the lack of any specific information from the crew regarding an explanation for the deviation from their flight plan, the evidence developed in the investigation permits a reasonable analysis of the circumstances surrounding the final maneuver.
The Board, in attempting to correlate the indications of the AC powered instruments with the final maneuver, concludes that the crew experienced an AC electrical failure and resultant loss of both primary attitude and heading references as well as the yaw damper, while flying on the assigned route. The pilots, faced with the extremely difficult task of controlling the aircraft under these circumstances during night, turbulent conditions, lost control of the aircraft and an upset occurred. The aircraft disappearance from radar very shortly after the deviation, and the impact attitude, indicate that the upset involved a very steep spiral. It is possible that total AC and DC electrical failure occurred during the descent, thereby resulting in the loss of radar reception of the transponder. However, it is believed more likely that the proximity of the last target to the crash site, and the inability of the controller to detect a primary return from the aircraft within seconds of the secondary target loss, indicates that the loss of radar
