In discussing the causes for the fire it is necessary to analyze the inflammable characteristics of various materials in that part of the airplane where the fire apparently started. Baggage and mail are obviously inflammable as is much of the buffet and lavatory equipment. Cabin interiors are lined with fabric treated to reduce inflammability. This treated material will not burn as readily as doped fabric but it is nevertheless inflammable. Soundproofing also will burn. raper probably burns the nest readily of all materials present in the Airplane cabin. During tests conducted subsequent to the accident by a government agency a fire of wrapping paper attained a temperature of over 1100° F. Inasmuch as the alloy used for skin and structural members of the DC-3 has a melting point under 1200°, it is apparent that paper alone could have been responsible for the burning of the metal in the rear of the fuselage during flight and that no other inflammable material need have been present.
The speed with which fire would spread within the fuselage of a DC-3 depends upon the presence and the direction of draughts. Two factors influence the air flow conditions; namely, the settings of the heating and ventilating systems and the opening or closing of doors and windows in the pilots' cockpit. Opening of doors tends to increase air circulation sharply. In general the direction of air flow is toward the front of the cabin. This condition is aggravated appreciably if the side windows in the pilots' cockpit are open. Thus, with a fire in the rear of the cabin or in the lavatory, open doors would accelerate its spread toward the front of the cabin. In view of the very definitely marked arcs of fire concentration it appears that the flow was not conducive to the spreading of the fire until portions of the lavatory and baggage compartment partitions were burned through.
While the source of the fire has not been determined, the portion of aircraft in which the fire originated has been fairly accurately established
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