Ullage Deflagration: Other tanks, other a/c makers
Fueldrinker asked about other tank deflagrations suffered by non-TBC airliners (above).
The AAR for TWA800 has an Appendix G that list some earlier cases, that cites Douglas cases (omitted many other examples).
The first modern investigation of an airliner ullage deflagration was in 1959, done by the Italian authority. That was Lockheed:
TWA 891 / 26Jun59, TWA Super Constellation L-1649-A N7313C flying near electrical storm. Broke-up in flight. Near Milan Italy, Vicinity of Olgiato Olona, Varese Province Italy....
... At disintegration altitude was between 11000' and 12000'; speed about 170 KIAS. Experiments concluded that critical variable existed for gasoline vapor ignition: tests in presence of non-static electrical discharge showed vapors ignite only if plane were CLIMBING. Uncertainty, vapor ignition tests only showed that "hazard cannot be excluded and vapors would actually ignite if the electrical discharge were non-static and sufficiently intense." Witnesses near site observed a lightning stroke, sound of explosion, then saw the fall of the plane's burning wreckage....
P.C. = from seven hypotheses , process of elimination discarded six; the remaining hypothesis deemed probable: Breakup due to explosion of fuel vapors in Fuel Tank #7, followed by excess pressure or further explosion in Tank #6; #7 Tank fuel vapors set-off by ignition of gasoline vapors from static electricity discharges (streamer corona) that developed at vent outlet.
Recommendation: More research and tests of fuel tank explosion, and instructions to pilots to avoid flight through such hazardous weather....
... Rpt of Board of Inquiry of Ministry of Defense, Republic of Italy, Rpt date Nov '60 (USA's CAA AAR File # 1-0045).]
= = = = / / / = = =
Here's another non-Boeing example:
British Eagle Int'l Airlines (BEIA) / 30Aug66 Britannia G-ARKA London, during pressure refueling at 0015 hrs an explosion occurred within starboard wing causing tank rupture and limited structural damage.
A/c had been on ground nine hours since flight, heavy rain at time of incident; crew onboard doing pre-flight checks. Few obvious ignition sources in region of tank, electrostatic discharge suspected within tank. First known incident of "ESD" in a civil a/c [numerous Canadian military a/c had suffered such tank explosions].
Conclusions from RAE Tech Rpt 67080, Apr'67, "Investigation into a Fuel Tank Explosion, Britannia G-ARKA" by M.E. Rogers & H.W.G. Wyeth reveal lack of evidence:
"... mist or foam generated by refuelling must have been ignited by an electrostatic discharge in the tank ullage. There is no positive evidence to support this choice of ignition source and, in fact, conditions seemed unsuitable for dangerous charge accumulation at the time of this incident. However all other ignition sources are discounted."
CRC Nov'75 "Aviation Fuel Safety" states this ullage as JetA vapors, low order tank explosion, moderate damage.
[The AAIB had several observers there at Calverton (wreckage collection at the old F-14 factory), Dave King managed to get co-workers to do a search, AAIB faxed that RAE rpt within a few hours. AAIB guys told us they were surprised that AAIB had passed that case to the RAE for investigation.]