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Air Cargo Industry Still Fighting Fuel System AD

New rules designed to guard against Boeing 757F fuel tank explosions offer no significant safety benefit, cargo industry says.

Major cargo airlines and the industry advocacy group Airlines for America (A4A) are fighting to derail an impending series of FAA airworthiness directives (AD), the first of which is set to be published in late March. That directive will mandate Boeing 757 freighter fuel system modifications to prevent potential explosions, and announcements for other aircraft models will follow. 

The proposed 757 rule will require cargo airlines—within 6 years—to separate wires used by the 757’s fuel quantity indication system (FQIS) to measure the amount of fuel in the aircraft’s center fuel tank. The FAA wants the wires that run between the FQIS processor and the center fuel tank, as well as other wires that pass through a main fuel tank, to be separated by 2 in. to prevent a short circuit that could travel into the tank and cause a spark. 

The NTSB determined that such a scenario—an external short circuit that propagated into a fuel tank through FQIS wires—is the most likely explanation for the downing of TWA Flight 800, a Boeing 747-100, in the Atlantic Ocean in 1996. The 757 wiring directive is the latest in a long list of responses to the crash: In addition to dozens of ADs aimed at safing fuel tank components for several aircraft types, the FAA in 2001 issued Special Federal Aviation Regulation (SFAR) 88, requiring airframers to reanalyze the design of fuel tank systems, and in 2008 the agency finalized a rule requiring passenger airliners to have fuel tank inerting systems by the end of 2017 to mitigate the threat. But all-cargo aircraft were exempt from the 2008 rule. 

A4A says the cargo carriers have already spent “tens of millions” of dollars over the past 20 years in fuel tank safety improvements, and that the new rule did not account for nearly $36 million in upgrades that the airlines spent for SFAR 88 and other post-TWA 800 changes, including 55 ADs and wiring maintenance program improvements. “There have been no incidents since [these changes] were implemented,” A4A said in a meeting with the FAA in December. “This provides direct evidence that FAA projections for additional incidents was overstated and that SFAR 88 changes have worked.” A4A also says the costs—which it estimates at $16 million for UPS alone if other Boeing models are eventually included—will make U.S. cargo operators less competitive in the global marketplace as no other countries are requiring the upgrades. 


The FAA estimates that the AD will affect 148 cargo aircraft, costing operators $4.7 million for the parts and labor to separate the wires. A4A says the actual costs will be three times higher in labor hours due to the variance in accessing the wires between different aircraft, and the fact that wiring maintenance “often disrupts other systems.” The advocacy group also says existing service bulletins allow for an increase in the separation of most wires by no more than 0.5 in. 

During the meeting in December, A4A, along with representatives from Atlas Air, UPS and FedEx, asked the FAA to reconsider the AD, which was first published in 2012 and reissued as a supplemental notice of proposed rulemaking last year. The discussions were considered “ex-parte,” or limited to the FAA obtaining more details on previously submitted comments since the rule has not been finalized and the public comment period closed in April 2015. 

“In light of FedEx’s financial and technical investment to mitigate the unsafe conditions in all areas, this AD is difficult to understand technically relative to the amount of mitigation that would be required, in light of a true assessment of the risk,” said the FedEx representative at the meeting. The UPS representative said the “situation is unique” because Boeing, which carried out the SFAR 88 fuel tank analyses, is “equally unsure of the goal because there is not a definitive design target.” 

In a May 2015 comment on the proposed rule, Boeing said it accepts the FAA’s requirement to provide design changes through new service bulletins, but the company maintains its position that “based on previously provided analysis, the risk level is less than extremely improbable. The AD is not necessary since the airplane design is safe.” Boeing had earlier elected not to provide the service bulletin, as it had already provided servicing information for 757 inerting systems, an acceptable means of complying with the AD, albeit a more expensive solution than the FQIS wiring option. Comments in the public docket since the first release of the proposed rule in 2012 had been largely negative, with Boeing, Airbus, A4A, FedEx, UPS and others requesting that the FAA withdraw the AD. 

Airbus, considering the FAA’s intent to issue similar actions for other legacy Boeing and Airbus aircraft, stated that the combination of events needed to cause an explosion are “extremely improbable or they would not produce sufficient energies to create an ignition,” and the fleets concerned are “small and getting smaller over the next years to come.” 

The FAA has been staunchly defending its actions however, leaving little hope that the agency will either withdraw the rule or reopen the public comment process. 

At the December meeting, an FAA official deflected the chiding from airlines that no other countries had issued a similar rule.  “If the FAA issues an AD it is expected that most, if not all, other authorities will follow,” said Jeffrey Duven, manager of the FAA’s Transport Aircraft Directorate in Seattle. 

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