Air Transport

The US Federal Aviation Administration wants Boeing to prove that the composite structures of the 787 will not propagate fires that may develop in inaccessible areas and that fumes from composites and any nearby thermal/acoustic insulation will not be toxic to passengers, writes John Croft.

The special certification conditions, published last week, are a result of the FAA's inexperience with large-scale use of new structures on an aircraft. The 787's wing, fuselage skin, stringers, spars and "most other structural elements of all major subassemblies of the airplane" are composite, according to the FAA. As such, the agency says the fuselage "cannot be assumed to have the fire resistance previously afforded by aluminium".

There are currently no standards for in-flight fire propagation with respect to an aluminium fuselage, says the FAA, as past investigations had shown that thin film covering the thermal/acoustic insulation, not the aluminium structure itself, had allowed fires to spread.

Those fires were typically caused by electrical issues, either short circuits, arcing caused by chafed wiring or ruptured ballast cases.

The FAA published a rule in 2003 requiring that the material be tested to more stringent flame propagation requirements.

Under the new proposal, Boeing will have to show the 787 will provide the equivalent level of in-flight survivability as a conventional aluminium fuselage aircraft, including resistance to flame propagation by both the structure and thermal/acoustic insulation.

Furthermore, the FAA says that "all products of combustion that may result must be evaluated for toxicity and found acceptable".