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not aimed at any specific aircraft. Consequently, only that portion of the program that appears to be relevant to the subject accident will be discussed.
One effort in this regard was a review by the Coordinating Research Council of all available data concerning the relative safety of Type A and Type B jet fuels and mixtures thereof. The group making this study concluded that while there are differences, the adoption of a single type of aviation turbine fuel by the entire industry would not significantly improve the overall excellent safety record of commercial aviation. The group further concluded that additional research into the nature and effect of lightning strikes and electro-static discharges is warranted and that more information is desirable regarding the phenomena of fuel spray, misting, and localized vapor-air mixtures in tanks under actual flight conditions. The Federal Aviation Agency is implementing research and test programs to accomplish, in the main, the Coordinating Research Council's recommendations.
It was demonstrated that direct lightning strikes to over wing filler caps and access plates of the configuration used on the aircraft in question can produce sparks inside of the fuel tank. No evidence of a direct strike was found on these parts from N709PA. Practical means whereby these potential hazards can be eliminated, as demonstrated within the limits of the testing facility, were developed and, in the case of access plates, have already been applied to aircraft in service. Testing failed to demonstrate any hazard from induced voltages in the fuel quantity measuring system. A complete wing section of essentially the same configuration as B707-121 was tested for internal parking in the reserve tank. Simulation of lightning strikes to the extent of the testing facility capability did not produce any recorded evidence of sparking within the tank.
The testing facility that was used is recognized as being among the most proficient in the field of lightning simulation and research. It is felt that the current state of the art does not permit and extension of test results to unqualified conclusions of all aspects of natural lightning effects. The need for additional research is recognized and additional programming is planned.
Probable Cause
The Board determines the probable cause of this accident was lightning-induced ignition of the fuel/air mixture in the No. 1 reserve fuel tank with resultant explosive disintegration of the left outer wing and loss of control.
BY THE CIVIL AERONAUTICS BOARD:
/s/ ALAN S. BOYD
Chairman
/s/ ROBERT T. MURPHY
Vice Chairman
/s/ CHAN GURNEY
Member
/s/ G. JOSEPH MINETTI
Member
Member
