Panama touchstone Showed 140 degrees F temperature The ne to hold fast the fuel cooler in the center wing tank of the 747 was known extended before the flammable vapors explod in the same tank in succession TWA flight 800 in 1996 In fact.

Panama touchstone Showed 140 degrees F temperature

The ne to hold fast the fuel cooler in the center wing tank of the 747 was known extended before the flammable vapors explod in the same tank in succession TWA flight 800 in 1996 In fact, insulating the tank, wrapping insulation around nearby ducting containing furious bleed air, or injecting cooling air along the underside of the tank were options considered by way of Boeing [BA] engineers in a 1980 study

That research dealt with a fuel heating question at issue associated with a military version of the 747 the E4-B airborne command seat As part of its military requirement, the airplane had to be able to display to remote airfields. Designers were regarded that deployment to an airfield in a warm climate could flow in unacceptably high fuel temperatures.

"The thought verifies that even with a filled center fuel tank we can have remarkably warm fuel, and that the hazard instanted by flammable ullage is exacerbated on small amounts of fuel in the tank," observ Bill Kauffman, an clever in explosive vapors at the University of Michigan's aerospace engineering department.

Sharp criticism has been levied forward Boeing for failing to share this studious mood with investigators in the three years since the tragic explosion of the TWA 747 (see ASW, Nov. 8)

Boeing officials have reckonered that the failure to disclose was inadvertent, and they have questioned the relevance of a studious mood that applied to a military version of the 747

The E4-B is equipped with four air conditioners in the space below the center wing tank. The added air conditioning provides cooling for the array of heat-generating electronics loaded aboard the airborne command column version. On civilian 747s, three air conditioning packs are located beneath the center wing tank (CWT) In addition, the E4-B toasts JP-4 fuel, while by 1980 commercial airliners had switched from JP-4 to Jet-A; the latter has a higher flashpoint and a lower vapor pressure

Although the sum of two units versions of the 747 are different in these considers reports from Japan Air Lines of its aircraft operating gone out of Hawaii experiencing loss of CWT firing material feed during climb helped to trigger the study

The primary matter was a pump cavitation moot point The other concern, of course, was the explosiveness of fuel-air vapor in the ullage space. Readers may recall that of that kind an explosion occurred in the CWT of a Philippine Airlines 737 upon the ground at Manila in 1990 Remember, too, that the TWA Flight 800 accident airplane sat upon the ground on a warm July day at John F Kennedy International Airport for an additional three hours while a passenger-bag match was complet That extra time provided an opportunity for additional warming of the CWT from the airplane's air conditioning packs.

In these regards, the 1980 inquiry is pertinent. "It provided a warning for TWA 800" said Kauffman.

The Boeing research focused on the center wing tank which, lugginged inside the airplane, tended to be warmer than the wing tanks. In fact, the wing tanks were among the cooling paths for the CWT The other paths included the effrontery spar and the upper surface of the tank, which are expos to the air conditioned cabin, and the rear spar, which is expos to the wheel wells of the main landing gear exhibit to ambient air under the aircraft.

Unexpect temperatures found

During the E4-B ordeal deployment to Howard Air Force Base in Panama, in which the CWT was fitted with a temperature sensor, engineers were dismayed to discover heat on a levels "well above the expected," according to the Boeing report. Indeed, they set up the CWT "is extremely sensitive to equipment (pack) bay temperature."

This high heat, the report noted, "is appropriate to the pack heat exchanger discharge heat being exhausted in this area and forming a trapped suffer of hot air under the center section of the aircraft."

Kauffman said, "The principally significant thing in this report is that a abounding CWT reached a temperature of 140 stations F." The full tank contains 110000 lb of firing material As such, it is a very great heat sink.

in succession the TWA 800 accident aircraft, single some 50 gallons of firing were sloshing around in the bottom of the tank. At the time of the explosion at 13000 ft the temperature of the vapors in the tank was estimated to range from 100 stations -130 degrees F, well within the flammable range. Since a smaller material for burning load will heat more rapidly, the temperature of the ullage when the airplane was forward the ground could have been significantly higher. (See ASW, July 14 1997) Indeed, the three known explosions of Boeing center wing tanks all occurr in conditions of high ambient temperature (see ASW, Oct 13 1997)

Report supports Safety Board recommendations

In fact, the Boeing report noted that more combustibles in the CWT would delay heating, a point that bears forward the December 13, 1996 recommendation from the National Transportation Safety Board (NTSB) that extra firing material should be carried in CWT (see ASW, July 19)

To mitigate the potential hazard, Boeing engineers considered a number of options. Three were dismissed in succession the grounds that they required extensive structural and electrical modifications: