FAA also said that since releasing the final insulation rule in July 2003, it realized that some requirements mandating upgraded material on replacement parts do not significantly improve airplane fire safety and that in many cases compliant replacements are not readily available. The Dec. 30 amendment, FAA said, "focuses on replacement materials that have a greater effect on safety and are readily available, and is necessary to avoid grounding of airplanes."

The new thermal requirements were proposed in 2000, following the 1998 crash of Swissair Flight 111. The Transportation Safety Board of Canada concluded that an electrical fire spread through flammable material aboard the McDonnell Douglas MD-11 and recommended more stringent flammability standards.

FAA's new flammability standards originally were believed to cover only thermal and acoustic blankets installed in aircraft operated under Part 121. But the agency in June released guidance that made it clear "that the rule was being applied to every insulating material in the fuselage of every Part 25 aircraft (both old and new) to include hard components, wiring bundles, tape, hook and loop fasteners (Velcro) and every piece of installed equipment with insulation," according to seven industry groups who co-signed a letter to FAA Administrator Marion Blakey last summer urging a delay in the rules. The groups said the rules would cover items such as microwave ovens, coffee makers, air ducting, avionics components and other commercial-off-the-shelf pieces that contain insulation.

The requirements, the groups told the administrator, "clearly exceed the scope of the [proposal] and what we believe was originally intended." This is problematic since compliance replacement parts are not available for many out-of-production airplanes, the groups said, adding that the rules should be limited to thermal and acoustic blankets used in Part 121 operations.

FAA agreed, that in light of some of the concerns raised, changes are necessary for a number of reasons. "Thermal/acoustic insulation is used much more extensively in the fuselage than we originally understood," the agency said, adding, "We did not consider whether compliance replacement parts could be efficiently produced for a significant number of parts installed on airplane models that are no longer in production." FAA also agreed that some materials required for compliance cost or weigh more than materials they replace. "This is particularly true for materials that are used to insulate certain equipment or provide acoustic attenuation in specialized application," the agency said, adding that a significant redesign would have been required to install the new materials.

FAA agreed to narrow the scope of the rule to cover primarily replacement of blankets and certain duct insulation on aircraft produced before Sept. 2, 2005. The agency, however, maintained the applicability to transport category aircraft operated under Parts 91, 135 and 121 - rather than limiting the requirements only to Part 121-operated aircraft. Insulation blankets, typically installed directly on the interior of the airplane fuselage, around ducts and under floor panels, "represent the largest usage of thermal/acoustic insulation in the airplane and are, therefore, the most significant from a fire safety standpoint," the agency said. Materials for insulation blankets are widely available "and can be readily adapted to different applications, even for airplane models no longer in production." FAA added that the insulation blanket standards were the primary driver for the rules in the first place.

Air Ducts

FAA also maintained that the new standards for insulation around ducts are necessary. "Ducts are intended to convey a fluid medium from one point to others and, therefore, provide a potential fire propagation path by their nature." But FAA added that it was limiting replacement requirements to air

 ducts only. "Other types of piping, or fluid lines are no longer covered by the replacement provision." The agency also said that insulation that is integral to the duct and cannot be replaced without replacing the duct is no longer covered. "This includes insulation that is bonded or laminated to the surface of the duct."

The rules do not cover new aircraft, the agency said, since "airframe manufacturers have worked diligently to achieve compliance for newly manufactured airplanes and all the affected parts have been addressed."

Industry groups were generally pleased with the FAA's amendment to the insulation rule. "It's now a much better rule than was written before," said Gregory Bowles, manager of engineering and maintenance for the General Aviation Manufacturers Association. "I think the FAA has done very well to balance safety" with the ability of the industry to meet the requirements, he said. The rule, however, serves as a reminder to industry to carefully examine FAA rulemaking. FAA stated that during the notice and comment period for the rules, it received little guidance about some of the problems that industry brought to light last summer.

The Aircraft Electronics Association also said it was pleased with the changes. "The amendment is very appropriate and reasonable," AEA said. AEA added, however, that is was disappointed that FAA did not address problems with parts catalogs that contain parts that the rule rendered unacceptable for use on U.S.-registered aircraft.

National Air Transportation Association echoed those comments, saying several of its concerns had been addressed. "However, the final rule does not address a significant compliance concern," the association said. "Hundreds of parts catalogs now contain part numbers that are no longer compliant with this rule."

The amendment takes effect Jan. 30, but FAA will accept comments on the changes through Feb. 28. Comments can be e-mailed to http://dms.dot.gov and should identify the docket number FAA-2005-23462.