Thermal insulation on all McDonnell Douglas DC-10s and Boeing MD-80s, MD-90s and MD-11s must be replaced within four years, the US Federal Aviation Administration has ordered.

The regulation has been under consideration for more than a year, but has become mandatory just as the Transportation Safety Board (TSB) of Canada releases interim recommendations on insulation materials. This follows findings in the Swissair MD-11 accident inquiry. The inquiry has recovered enough of the metallised Mylar (polyethylene terephthalate) insulation from the cockpit area to deduce that the material played a part in "sustaining" the fire which brought down the MD-11 off Nova Scotia in September last year. The ignition source is suspected to have been faulty wiring, however.

TSB safety recommendations following the investigation state: "There are indications that a significant source of combustible materials that sustained the fire were thermal acoustical insulation blanket material." The board calls for its urgent replacement.

The order affects 700 US-registered aircraft, but if foreign authorities follow the FAA, an additional 530 aircraft could be involved. The cost to US operators is $255 million, according to FAA estimates.

Insulation replacement should take place at the earliest heavy maintenance visit, the FAA says. Potential alternative insulation blanket materials include non-metallised Mylar, metallised Tedlar (polyvinyl fluoride) and a polyester-covered foam known as Teril 34.

The action will not lead to a tougher specification for other types of aircraft insulation. The FAA had originally proposed this, then backed off following industry protest, as it could have led to insulation replacement in up to 12,000 commercial aircraft worldwide.

Source: Flight International