Calls Explosion Risk 'Less Than Extremely Improbable'

In the wake of an explosion aboard a TWA Boeing 747 in 1996, the FAA has proposed that Boeing retrofit the fuel tank wiring in 352 B757 cargo jets operating in the U.S. But Boeing, A4A, UPS and FedEx are all opposed to the measure.

The Seattle Times reports that Boeing officials said that the risk of an explosion caused by the wiring in the fuel tanks is "negligible." The company has balked at the wiring modification the FAA says should be installed on 757s already in service.

An NPRM, which was published in the Federal Register June 5th, refers to previously-proposed rule published in the Federal Register on March 1, 2012 (77 FR 12506). That NPRM proposed to require modifying the fuel quantity indication system wiring or fuel tank systems to prevent development of an ignition source inside the center fuel tank.

That action, which invites comments on regulatory, economic, environmental, and energy aspects of the proposal was prompted by fuel system reviews conducted by the manufacturer. The actions specified by the NPRM are intended to prevent ignition sources inside the center fuel tank, which, in combination with flammable fuel vapors, could result in fuel tank explosions and consequent loss of the airplane.

The FAA said in the Federal Register that it had received a request from Airlines for America (A4A), and James Hurd on behalf of the Families of TWA Flight 800, to extend the comment period. A4A requested a 60-day extension because of the extensive scope and significant potential impact of the NPRM, the lack of associated service information, and the need for proper review of the results of prototype efforts.

A4A stated that this extension would provide operators additional time to develop estimates of technical methods of compliance with the NPRM, to develop estimates of the potential impact of those methods, and to prepare comments for the rules docket. The FAA said it was appropriate to extend the comment period to give all interested persons additional time to examine the proposed requirements and submit comments, and that extending the comment period by 60 days will not compromise the safety of the affected airplanes.

The Seattle Times reports that modifications have already been mandated for passenger jets, though certification issues have delayed installation of the modification kits on about 2,000 airplanes, according to A4A spokesman Steve Lott. The new rule would expand the requirement for the installation of nitrogen generating systems (NGS) for fire suppression to cargo jets, which had previously been exempt.

Boeing, Airbus, A4A, UPS, and FedEx are all opposed to a requirement forcing the modifications to cargo planes. But other organizations, such as NATCA, say that not only should cargo planes be included, but that the modifications should be required on the wing tanks of all 757s, not just the center fuel tank, and that the period for compliance should be shortened from five years to three.

A wiring fix proposed by Boeing is reportedly more expensive than the one the AD would mandate ... over $200,000 per airplane, according to Boeing.The planemaker estimates that the probability of a failure caused by the existing wiring configuration of the center fuel tank probes which provide fuel quantity data to the cockpit on any given 757 to be about one in a billion per flight hour, and it says the risk is even lower for cargo planes. Given that statistical probability, and the average age of the fleet, Boeing says that "a risk this low does not require further mitigation."

The comment period closes August 6th.

FMI: NPRM