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be expected to cause a fire that would progress outward and heat this tube sufficiently to ignite the fuel/air mixture in the No. 1 reserve tank prior to failure of the wing farther inboard. A leak in the general vicinity of the transfer tube could possibly produce this result, but the fire could not be expected to progress through the trailing edge almost to the fuselage causing the observed inflight fire damage prior to failure of the wing near the source of the fire.
In addition, the metal splatter on the left horizontal stabilizer leading edge and inflight fire damage to the left elevator could occur only after loss of the left outer wing. In normal flight, the airflow over the wing and materials separating from the wing trailing edge pass well below the horizontal tail rather than striking it and do not have the sideward component of travel displayed by the metal splatters. Also, the fire damage high on the left side of the vertical tail is wholly incompatible with fire emanating from the wing trailing edge under any normal flight conditions.
From the facts of the investigation, it has been determined that explosions occurred in the left reserve, center, and right reserve fuel tanks. The wreckage distribution supported by the fire damage pattern, leads to the conclusions that the initial explosion was in the left reserve tank and that no fire-damaged part separated from the aircraft prior to the explosion.
The exact sequence and timing of the subsequent explosions and inflight fires are not known and are, in fact, somewhat academic with respect to the probable cause of the accident. Fires were observed on both wings of the aircraft before impact. It is logically concluded that the main tanks which contained fuel and are adjacent to the reserve and center tanks were structurally disrupted when some or all of the aforementioned tanks exploded; fuel was spilled and ignited. Such spillage from the opened outer end of the No. 1 main tank and fire damage to parts after thereof, including the still attached inner ends of the outer panel rear spar and outboard aileron, are quite apparent. Early separation of the outboard engines in the sequence of events may have contributed, at least in part, to the large fires that were observed on the wings.
Although much effort was expended, the physical evidence failed to disclose the precise mechanism of ignition which triggered the explosion in the left reserve fuel tank. However, witnesses, some particularly well qualified, observed a cloud to earth lightning discharge, described as being of exceptionally great magnitude, in the immediate location from which, moments later, the burning aircraft emerged. Before observing the aircraft, a glow or light was observed in near proximity to the location of the lightning discharge. Consequently, there is a direct correlation in time and location between the lightning discharge and start of events which culminated in the accident.
Lightning discharge damage judged to be of recent origin and of an extent compatible with the reportedly observed massive lightning stroke was observed in several locations at the left wing tip area. It is pertinent to note, however, that none of the damage was on wing skin that encompassed fuel tank or vent system space of the aircraft; consequently, a direct correlation of any of this damage with the tank explosion is not possible.
Extensive and meticulous effort was expended attempting to find evidence of an electrical discharge that may have ignited the flammable mixture in the left reserve
