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Thermal/Acoustic Insulation Installed on Transport Category Airplanes

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Federal Aviation Administration (FAA), DOT.


Disposition of comments on final rule.


On December 30, 2005, the FAA published a final rule; request for comments (Amendment Nos. 91-290, 121-320, 125-50, and 135-103), on the requirements for thermal/acoustic insulation flammability (70 FR 77748). We sought public comments on those amendments, but they became effective on February 28, 2006. This action responds to the comments received on that final rule; request for comments.


You may review the public docket (Docket No. 2005-23462) in the Docket Management Facility between 9 a.m. and 5 p.m., Monday through Friday, except Federal holidays. The Docket Management Facility is on the plaza level of the Nassif Building at the Department of Transportation, Room Plaza 401, 400 Seventh Street, SW., Washington, DC 20590-0001. Also you may review the public docket on the Internet at

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Jeff Gardlin, Airframe and Cabin Safety Branch (ANM-115), Transport Airplane Directorate, Aircraft Certification Service, Federal Aviation Administration, 1601 Lind Avenue, SW., Renton, Washington 98055-4056; telephone (425) 227-2136, facsimile (425) 227-1149, e-mail:

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On September 20, 2000, the FAA published Notice No. 00-09, which proposed to upgrade the flammability and fire protection standards for thermal/acoustic insulation installed in transport category airplanes (65 FR 56992). The notice contained a provision that would require thermal/acoustic insulation to comply with the proposed new standards when used as replacements on airplanes already in service, as well as requirements about newly manufactured airplanes. The requirement was adopted in the final rule, published on July 31, 2003, in §§ 91.613(b)(1), 121.312(e)(1), 125.113(c)(1), and 135.170(c)(1) (68 FR 45046). These rules required operators to use replacement insulation materials meeting the requirements of § 25.856 after September 2, 2005.

For reasons discussed in the preamble, we published Amendment Nos. 91-290, 121-320, 125-50, and 135-103 on December 30, 2005, to refocus the requirements for replacement materials (70 FR 77748). Because of these amendments, only certain types of thermal/acoustic insulation are required to comply with the upgraded standards when replaced. As noted in the preamble, the revised requirements align the regulatory language more closely with the intent of the provision.

Although the immediately adopted rule revised the replacement provisions, we requested comments on the provisions. Six commenters responded to the request for comments.

Discussion of Comments

The General Aviation Manufacturers Association and Continental Airlines support the rule as written. AMIS International provided comments that were not directed at the substance of the amendments. Airbus, Boeing and the National Air Transport Association (NATA) support the rule, but suggest further changes as well.

Boeing suggests we further amend the rules so the requirements of 14 CFR part 25 match the revised requirements for replacement materials. The FAA does not agree. The intent of the part 25 rule is to upgrade the standards for thermal/acoustic insulation in the fuselage of transport category airplanes. Advisory Circular 25.856-1, Thermal/Acoustic Insulation Flame Propagation Test Method Details, dated 6/24/05, provides discussion and methods of compliance for specific installations that simplify the compliance demonstration. Conversely, the provision on replacement thermal/acoustic insulation is intended to address insulation that is often replaced. The objective of that requirement is to encourage production only of materials that comply with the new standards, as well as to purge inventories of materials that do not comply. Thus, the two provisions are complementary, and need not be the same. Since manufacturers are producing airplanes that comply with the existing requirements of § 25.856(a), the requirements are clearly feasible. Changing part 25 as requested would reduce the level of safety already achieved.

Boeing further suggests the definition of insulation provided in the final rule be included in Advisory Circular 25.856-1 and possibly § 25.856(a) to be consistent. The FAA does not agree. Amendment 91-290 et al., does not “define” insulation. These amendments modify the applicability of requirements for insulation. That is, they specify the conditions under which we require compliance with § 25.856(a) for replacement thermal/acoustic insulation. Thus, we require no changes to the advisory circular since it pertains to compliance with § 25.856(a), and does not apply if compliance with § 25.856(a) is not required.

Boeing also suggests we change the rule to exclude blanket type insulation installed inside galley inserts or other components. These components can be replaced and it is not obvious the replacement includes insulation. The FAA does not agree. Advisory Circular 25.856-1 already addresses these components, and describes a means of compliance that does not necessitate testing in most cases. Since compliant materials are available for those cases when testing is required, the rule should remain as is.

Airbus similarly suggests we change the replacement provision to exclude blanket type insulation when bonded to interior panels, such as sidewalls or floors. Airbus notes that these are infrequently replaced and it would be difficult to change the insulation. The FAA does not agree. Although the insulation is bonded to these panels, if it is in blanket form, there are available substitutes that comply. As long as operators are aware of the particular parts that are affected, they can accommodate the upgraded materials into their maintenance plan.

Airbus also notes that it used many resources to modify its affected parts and drawings before the compliance date, and now some of that effort appears wasted. Because the issues with replacement insulation were identified very late in the process, the FAA acknowledges that Airbus' proactive Start Printed Page 52288approach probably did result in changes that ultimately were not strictly required for compliance. However, these changes do improve the overall flammability of the materials and are not wasted effort.

The NATA concurred with the rule, but was concerned the now outdated part numbers associated with non-complying parts have not been purged from parts catalogs. The NATA requests the FAA help industry deal with the issue of out of date parts catalogs. Parts catalogs are not directly regulated documents, and the FAA does not typically maintain oversight of them. However, the FAA will work with operators and airframe manufacturers to help facilitate updating of the parts catalogs.

Boeing suggested a rewording of the preamble discussion of insulation that is the subject of airworthiness directives as follows: “Insulation that is the subject of airworthiness directives (even if that insulation is bonded to the surface of the duct and would otherwise be excluded by this rule) must still be replaced in accordance with those airworthiness directives.

While the FAA acknowledges the suggested rewording is more explicit, the intent is the same. This discussion in the preamble was purely a reminder, and does not introduce a requirement or deviate in any way from standard procedure. No change to the rule is required.


After consideration of the comments submitted in response to the final rule; request for comments, the FAA has determined that no further rulemaking action is necessary and Amendments Nos. 91-290, 121-320, 125-50, and 135-103 remain in effect as adopted.

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Issued in Washington, DC, on August 25, 2006.

John J. Hickey,

Director, Aircraft Certification Service.

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[FR Doc. E6-14632 Filed 9-1-06; 8:45 am]