Ramon Lopez/WASHINGTON DC
Within six months, the US Federal Aviation Administration is to produce a tougher burn test specification for aircraft internal insulation blankets. The action results partly from investigations into the 2 September crash of a Swissair Boeing MD-11 off Nova Scotia. Although the cause of the fatal accident remains a mystery, the possibility of an electrical fire sparked by faulty wiring and fuelled by insulation is one theory under investigation.
The FAA is already urging Airbus Industrie, Boeing and other manufacturers, as well as the US Air Transport Association and Regional Airline Association member carriers, "-to take advantage of any reasonable maintenance opportunity" to replace the insulation blankets. A series of fires prompted McDonnell Douglas to recommend in 1997 that the material be replaced at "the earliest practical maintenance period". One of those incidents involved a China Eastern Airlines MD-11, which caught fire on the ground after an inadequately secured wire bundle in the avionics bay rubbed against a fuselage frame, causing arcing.
The FAA has warned that additional service bulletins, new maintenance practices and airworth- iness directives may be issued to reduce the fire threat while new standards are being developed.
Preliminary research has already identified materials that provide "a substantial increase" in fire resistance over materials now in use, says the FAA. These include glassfibre and a material known as Curlon. Each is wrapped in a polyimide film. Polyimide is the chemical name for compounds such as Dupont's Kapton that have high heat resistance characteristics.
Neither the FAA nor the airline industry can say what the safety initiative will cost. The long-term action will not be disruptive since the work will take place during regular major overhauls.
Boeing uses non-metallised Mylar and metallised Tedlar insulation, which company officials say will not comply with the more stringent burn standards. Airbus uses a polyester-covered foam known as Teril 34. The FAA says that Boeing insulation would burn under certain circumstances, and that Airbus insulation did not perform well in testing. The Lockheed L-1011 TriStar appears to have been constructed with acceptable insulation.
Source: Flight International
