Boeing is aiming for certification of a fuel tank inerting system on the 747 by the end of next year or early in 2005. Eight flights of a prototype will be completed this month on a 747-400 testbed, and the data used to refine the design of the flammability reduction system (FRS). A production system will then be installed on another 747 for certification.

A scaled-down FRS will be installed on a Next Generation 737 for flight tests beginning by early 2004. Boeing plans to certificate centre wing-tank inerting systems in all 7-series airliners by the end of 2006, or early in 2007, says programme manager Mike Delaney.

Inerting of all tanks is being designed into the 7E7 from the outset, he says. Boeing is to fit systems in some 737s and 747s for in-service evaluation after certification.

The FRS uses a nitrogen generating system supplied by Honeywell, partnered with Parker Aerospace. Engine bleed air is ducted to air separation modules that remove oxygen and deliver nitrogen-enriched air to the tank to reduce the flammability of fuel vapour. The aircraft manufacturer intends to make the inerting system available for retrofit as a service bulletin, but pricing has not been determined, says Delaney.

The US Federal Aviation Administration will decide whether to mandate installation of inerting systems based on data from Boeing and Airbus tests as well as work under way to eliminate ignition sources from fuel tanks.

The 747 FRS has five air separation modules. One is used in climb and cruise, and all five in descent when the flammability risk is highest. The 737 has one larger module, while the 757 and 767 require four and the 777 six.

FAA Technical Center tests last year determined an oxygen level of 12%, rather than the 10% previously assumed, is sufficient to prevent ignition. This halved the inerting system's size, making it commercially viable.

Source: Flight International