Mr. George S. Moore
Director
Flight Standards Service
Federal Aviation Agency
Washington, D. C., 20553
Dear Mr. Moore:
The investigation to date of the Pan American World Airways, Inc., Boeing 707-121, N709PA, aircraft accident near Elkton, Maryland on December 8, 1963, has identified in a gross sense the causal areas. That an inflight explosion occurred in the No. 1 reserve fuel tank is readily evident. It is believed the explosion stemmed from ignition of combustible fumes at the fuel tanks vent outlet by a lightning strike. Positive evidence of lightning striking in the wing tip area, some near the vent system outlet, has been noted. The investigation, to attempt to more precisely define the mechanism of initial ignition and progress to explosion, is continuing.
Fuel aboard at the time of the accident was approximately a 68/32 Jet A/Jet B by volume mix. Based on data furnished by PAWA, it is estimated the temperature of the fuel was approximately 42 degrees F. Except for normally unuseable fuel, all was being carried in the four main tanks. Considering all factors, it is concluded the fuel vapors in all tanks were within the flammability limits.
This accident has focused attention on a serious problem; not new as evidence by the studies previously made and the great number of reports and papers dealing with it. There is no doubt in our mind that our concern regarding this matter is shared equally by yourself and staff. It is appreciated also that immediately attainable corrective measures to provide total protection are not readily evident. However, we do feel and urge that all available government and industry resources should be marshalled to implement protective measures. Even partial measures effecting direct improvement appear warranted before the ultimate protection can be provided.
The following recommendations for your consideration are submitted:
- Install static discharge wicks on those turbine powered aircraft not so equipped.
