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Subsequent investigation disclosed that the aircraft skidded approximately 646 feet before coming to a stop. All four propellers were damaged and the 12 blades were bent back at an angle of approximately 85 degrees. The cowling and engine mounts on No. 2 and No. 3 engines were badly damaged. The landing gear and two inboard oil tanks were also damaged, as well as the under surface of the fuselage.
The carburetor air heating system on this airplane took warm air from the rear engine compartment only when the carburetor was set at full heat. This, through the experience and recommendation of the engine and airplane manufacturers, was deemed sufficient to provide a minimum of 40° F. heat rise of the intake air when the outside temperature was 32° F. This met with Civil Aeronautics Authority regulations for heat rise in connection with the non-icing cam type Venturi carburetor with which these engines were equipped. Actual tests indicated that on this installation a heat rise of 46° F. was available at full-heat setting.
The engine cowl flaps of all four engines were connected to a common control in the cockpit. Through some maladjustment of linkage, the cowl flaps of No. 2 engine (left inboard) were more nearly closed than on the other three engines. Inasmuch as at full heat the carburetor air is drawn from the rear engine compartment, the position of the cowl flaps influence carburetor heat through the variation of the compartment temperature. The greater heat available on No. 2
