Aviation Investigation Report A98H0003

4.1.3  Thermal Acoustic Insulation Materials

  1. - Transportation Safety Board of Canada
  2. - United States Federal Aviation Administration
  3. - Transport Canada
  4. - Swissair
  5. - Swiss Federal Office for Civil Aviation  Transportation Safety Board of Canada

As of August 1999, the SR 111 investigation had revealed fire damage in the ceiling area forward, and several metres aft, of the cockpit wall. There were clear indications that a significant source of the combustible materials that sustained the fire was thermal acoustic insulation blanket (insulation blanket) materials. Burnt remnants of this material, caused by the in-flight fire, were found in the wreckage; the fire was extinguished upon impact with the water.

Shortcomings related to the in-service fire resistance of some thermal acoustic insulation materials, and weaknesses in the test criteria used to certify those materials, have been identified during this and other recent aircraft occurrence investigations. Subsequently, the TSB issued recommendations (A99-07 and A99-08) dealing with the risks associated with the flammability of metallized polyethylene terephthalate (MPET)–covered insulation blankets and the test criteria that certified this material for aircraft use.

The in-service history; the demonstrated flammability of the MPET cover material; and the discovery, in the SR 111 wreckage, of remnants of insulation blankets with burnt cover material suggest that MPET cover material was a significant source of the combustible materials that propagated the fire. It is the TSB's view that the operation of aircraft outfitted with insulation blankets incorporating MPET cover material constitutes an unnecessary risk. Therefore, the TSB made the following recommendation:

Regulatory authorities confirm that sufficient action is being taken, on an urgent basis, to reduce or eliminate the risk associated with the use of metallized PET-covered insulation blankets in aircraft. A99-07 (issued 11 August 1999) (STI4-10)

A review of incidents involving cover materials other than those involving MPET (e.g., non-metallized polyethylene terephthalate) polyester film revealed that the limitations of Federal Aviation Regulation (FAR) 25.853, Appendix F, test criteria may not be confined to its inability to accurately and reliably identify the flammability characteristics of MPET-type cover material.

On 14 October 1998, the FAA stated that the test criteria used to certify the flammability characteristics of thermal acoustic insulation materials were inadequate, and committed itself to conduct the research necessary to establish a more comprehensive test standard. At the same time, the FAA indicated that because materials containing polyimide film have performed well in preliminary flammability tests, these materials would be considered compliant under the new regulation. Until adequate flammability test criteria are available, it is not possible to determine whether polyimide film, or other materials, provide adequate protection against fire propagation. Thermal acoustic insulation materials are installed in aircraft as a system, including such related components as tape, fasteners, and breathers. The TSB believed that thermal acoustic insulation materials for use in aircraft must be judged against more valid flammability test criteria—not as individual components, but as a system. Therefore, the TSB made the following recommendation:

On an urgent basis, regulatory authorities validate all thermal acoustical insulation materials in use, or intended for use, in applicable aircraft, against test criteria that are more rigorous than those in Appendix F of FAR 25.853, and similar regulations, and that are representative of actual in-service system performance. A99-08 (issued 11 August 1999) (STI4-11)  United States Federal Aviation Administration

The FAA responded to TSB recommendation A99-07 by issuing two NPRMs (99-NM-161-AD and 99-NM-162-AD). The NPRMs proposed the removal of MPET-covered insulation blankets from all US-registered aircraft. The final rule regarding these proposals came in May 2000 when the FAA issued two ADs (AD 2000-11-01 and AD 2000-11-02 available at http://www.faa.gov), which required the removal of all MPET-covered insulation blankets. These ADs were based on existing McDonnell Douglas (MD) SBs, which call for the replacement of the MPET-covered insulation blankets.

In response to TSB recommendation A99-08, the FAA accelerated a project to develop an improved certification flammability test for all thermal acoustic insulation materials. An NPRM (Docket FAA-2000-7909; Notice 00-09) was issued in September 2000 and the final rule is on hold pending a plain language review and rewrite. In the interim, the FAA issued Flight Standards Information Bulletin for Airworthiness 00-09 to ensure that 14 Code of Federal Regulations (CFR) Parts 121 and 125 operators have established procedures for the inspection of thermal acoustic insulation materials for any contamination during heavy maintenance checks.  Transport Canada

Although there are currently no aircraft in the Canadian register built with MPET-covered insulation blankets, TC conducted a survey to confirm that no Canadian-registered aircraft had used MPET-covered insulation blankets during a wholesale replacement program. Additionally, they worked with Bombardier Inc. to remove MPET-type tape from their RJ Series 700 specification.  Swissair

Prior to issuing the FAA ADs regarding MPET-covered insulation material, Swissair worked with Boeing to identify the high-risk areas of the MD-11 aircraft and by March 2001 had voluntarily replaced selected MPET-covered insulation blankets. Upon receipt of the FAA's AD 2000-11-02, Swissair began a complete MPET-covered insulation blankets replacement program on their MD-11 fleet. As of January 2003, the AD had been accomplished on 11 MD-11s previously owned by Swissair.  Swiss Federal Office for Civil Aviation

The Swiss FOCA reviewed and reissued AD 2000-11-02 as a   Swiss AD 2000-414.

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