Airworthiness Directives; Boeing Model 737, 747, 757, and 767 Series Airplanes

AGENCY:

Federal Aviation Administration, DOT.

ACTION:

Notice of proposed rulemaking (NPRM).

SUMMARY:

This document proposes the adoption of a new airworthiness directive (AD) that is applicable to certain Boeing Model 737, 747, 757, and 767 series airplanes. This proposal would require rework of certain duct assemblies of the environmental control system (ECS) or replacement of the duct assemblies with new or reworked duct assemblies. This action is necessary to prevent potential ignition of fiberglass insulation material installed on the outside of the ECS ducts, which could propagate a small fire and lead to a larger fire. This action is intended to address the identified unsafe condition.

DATES:

Comments must be received by September 25, 2000.

ADDRESSES:

Submit comments in triplicate to the Federal Aviation Administration (FAA), Transport Airplane Directorate, ANM-114, Attention: Rules Docket No. 2000-NM-226-AD, 1601 Lind Avenue, SW., Renton, Washington 98055-4056. Comments may be inspected at this location between 9:00 a.m. and 3:00 p.m., Monday through Friday, except Federal holidays. Comments may be submitted via fax to (425) 227-1232. Comments may also be sent via the Internet using the following address: 9-anm-nprmcomment@faa.gov. Comments sent via fax or the Internet must contain “Docket No. 2000-NM-226-AD” in the subject line and need not be submitted in triplicate. Comments sent via the Internet as attached electronic files must be formatted in Microsoft Word 97 for Windows or ASCII text.

The service information referenced in the proposed rule may be obtained from Boeing Commercial Airplane Group, P.O. Box 3707, Seattle, Washington 98124-2207. This information may be examined at the FAA, Transport Airplane Directorate, 1601 Lind Avenue, SW., Renton, Washington.

FOR FURTHER INFORMATION CONTACT:

James Cashdollar, Aerospace Engineer, Airframe Branch, ANM-120S, FAA, Seattle Aircraft Certification Office, 1601 Lind Avenue, SW., Renton, Washington 98055-4056; telephone (425) 227-2785; fax (425) 227-1181.

SUPPLEMENTARY INFORMATION:

Comments Invited

Interested persons are invited to participate in the making of the proposed rule by submitting such written data, views, or arguments as they may desire. Communications shall identify the Rules Docket number and be submitted in triplicate to the address specified above. All communications received on or before the closing date for comments, specified above, will be considered before taking action on the proposed rule. The proposals contained in this notice may be changed in light of the comments received.

Submit comments using the following format:

• Organize comments issue-by-issue. For example, discuss a request to change the compliance time and a request to change the service bulletin reference as two separate issues.
• For each issue, state what specific change to the proposed AD is being requested.
• Include justification (e.g., reasons or data) for each request.

Comments are specifically invited on the overall regulatory, economic, environmental, and energy aspects of the proposed rule. All comments submitted will be available, both before and after the closing date for comments, in the Rules Docket for examination by interested persons. A report summarizing each FAA-public contact concerned with the substance of this proposal will be filed in the Rules Docket.

Commenters wishing the FAA to acknowledge receipt of their comments submitted in response to this notice must submit a self-addressed, stamped postcard on which the following statement is made: “Comments to Docket Number 2000-NM-226-AD.” The postcard will be date stamped and returned to the commenter.

Availability of NPRMs

Any person may obtain a copy of this NPRM by submitting a request to the FAA, Transport Airplane Directorate, ANM-114, Attention: Rules Docket No. 2000-NM-226-AD, 1601 Lind Avenue, SW., Renton, Washington 98055-4056.

Discussion

The FAA has received reports that fiberglass insulation material installed on the outside of the ducts of the environmental control system (ECS) on certain Boeing Model 737, 747, 757, and 767 series airplanes does not meet fire safety requirements. During fire testing, samples of fiberglass insulation from the ECS ducts, with BMS8-142 vapor barrier bonded to the outer surface of the insulation with BAC5010 Type 97 adhesive, burned at a rate faster than allowed by section 25.853 (“Fire Protection: Compartment Interiors”) of the Federal Aviation Regulations (14 CFR 25.853). This condition, if not corrected, could result in potential ignition of the fiberglass insulation installed on the ECS ducts, which could propagate a small fire and lead to a larger fire.

Other Relevant Rulemaking

On May 19, 2000, the FAA issued AD 2000-11-01, amendment 39-11749 (65 FR 34322, May 26, 2000), which is applicable to certain McDonnell Douglas Model DC-9-80 and MD-90-30 series airplanes and Model MD-88 airplanes; and AD 2000-11-02, amendment 39-11750 (65 FR 34341, May 26, 2000), which is applicable to certain McDonnell Douglas Model DC-10-10F, DC-10-15, DC-10-30, DC-10-30F, DC-10-40, MD-11, and MD-11F series airplanes. These AD's require determination of whether, and at what locations, insulation blankets made of metallized polyethyleneteraphthalate (MPET) are installed, and replacement of any MPET insulation blankets with new blankets made of metallized Tedlar or equivalent blanket material. Those AD's were prompted by reports of fires (in flight and on the ground) on certain airplanes equipped with MPET insulation blankets. Such insulation blankets could propagate a small fire that is the result of an otherwise harmless electrical arc, and could result in a much larger fire.

The unsafe condition addressed by those AD's is similar to that addressed in this proposed AD. The fiberglass insulation with BMS8-142 vapor barrier bonded to the outer surface with BAC5010 Type 97 adhesive, which is the subject of this AD, can be ignited by a small ignition source and propagate a fire in a manner similar to the MPET insulation blankets. AD 2000-11-01 and AD 2000-11-02 require replacement of MPET insulation blankets with new blankets; this proposed AD would require rework of the ECS duct assemblies or replacement of the duct assemblies with new or reworked duct assemblies. The FAA finds that rework of the duct assemblies will ensure an acceptable level of safety for the affected airplanes addressed in this proposed AD.

A similar unsafe condition exists in drip shields on certain Boeing Model 747, 757, 767, and 777 series airplanes. Some drip shields are assembled with the moisture barrier cover bonded to the insulation and multiple insulation layers bonded together using a non-flame-resistant adhesive. Such assembly of the drip shield reduces the fire resistance of the moisture barrier cover and insulation. As a result, the drip shield assemblies do not meet the requirements of section 25.853 (“Fire Protection: Compartment Interiors”) of the Federal Aviation Regulations (14 CFR 25.853). This condition, if not corrected, could result in potential ignition of the moisture barrier cover of the drip shield, which could propagate a small fire that results from an otherwise harmless electrical arc, leading to a larger fire. A separate rulemaking action [notice of proposed rulemaking, Rules Docket No. 2000-NM-217-AD] is being issued to address that unsafe condition on affected airplanes.

Explanation of Relevant Service Information

The FAA has reviewed and approved Boeing Alert Service Bulletins 737-21A1129, 747-21A2416, 757-21A0084, 757-21A0085, and 767-21A0158; all including Appendices A and B; all dated June 29, 2000. Those service bulletins describe procedures for rework of certain ECS duct assemblies or replacement of the duct assemblies with new or reworked duct assemblies. The rework involves replacement of existing fiberglass insulation with new insulation. Accomplishment of the actions specified in the service bulletins is intended to adequately address the identified unsafe condition.

Explanation of Requirements of Proposed Rule

Since an unsafe condition has been identified that is likely to exist or develop on other products of this same type design, the proposed AD would require accomplishment of the actions specified in the applicable service bulletin described previously, except as discussed below.

Differences Between Proposed Rule and Service Bulletins

Operators should note that the service bulletins specify that the rework or replacement of the ECS ducts is to be accomplished at the next heavy maintenance check. The FAA finds that such a compliance time will not ensure that the rework or replacement is accomplished in a timely manner. In developing an appropriate compliance time for this AD, the FAA considered not only the manufacturer's recommendation, but the degree of urgency associated with addressing the subject unsafe condition, as well as the compliance time for the actions required by the previously described AD 2000-11-01 and AD 2000-11-02. AD 2000-11-01 and AD 2000-11-02 require replacement of MPET insulation blankets on affected airplanes within five years after June 30, 2000 (the effective date of those AD's). In light of all of these factors, and especially the similarity of the unsafe condition addressed in this proposed AD to that addressed in the AD's described previously, the FAA finds a compliance time of five years after the effective date of this AD for initiating the proposed actions to be warranted, in that it represents an appropriate interval of time allowable for affected airplanes to continue to operate without compromising safety.

Cost Impact

There are approximately 1,162 airplanes of the affected design in the worldwide fleet. The FAA estimates that 403 airplanes of U.S. registry would be affected by this proposed AD. The following table shows the estimated cost impact of the proposed actions for airplanes affected by this AD. The average labor rate is $60 per work hour. The estimated total cost for all airplanes affected by this proposed AD is $2,552,996.

The cost impact figures discussed above are based on assumptions that no operator has yet accomplished any of the proposed requirements of this AD action, and that no operator would accomplish those actions in the future if this proposed AD were not adopted. The cost impact figures discussed in AD rulemaking actions represent only the time necessary to perform the specific actions actually required by the AD. These figures typically do not include incidental costs, such as the time required to gain access and close up, planning time, or time necessitated by other administrative actions.

The manufacturer has advised the FAA that warranty remedies may be available for parts and labor costs associated with accomplishing the actions that would be required by this proposed AD. Therefore, the future economic cost impact of this rule on U.S. operators may be less than the cost impact figures indicated above.

Regulatory Impact

The regulations proposed herein would not have a substantial direct effect on the States, on the relationship between the national Government and the States, or on the distribution of power and responsibilities among the various levels of government. Therefore, it is determined that this proposal would not have federalism implications under Executive Order 13132.

For the reasons discussed above, I certify that this proposed regulation (1) is not a “significant regulatory action” under Executive Order 12866; (2) is not a “significant rule” under the DOT Regulatory Policies and Procedures (44 FR 11034, February 26, 1979); and (3) if promulgated, will not have a significant economic impact, positive or negative, on a substantial number of small entities under the criteria of the Regulatory Flexibility Act. A copy of the draft regulatory evaluation prepared for this action is contained in the Rules Docket. A copy of it may be obtained by contacting the Rules Docket at the location provided under the caption ADDRESSES.

List of Subjects in 14 CFR Part 39

• Air transportation
• Aircraft
• Aviation safety
• Safety

The Proposed Amendment

Accordingly, pursuant to the authority delegated to me by the Administrator, the Federal Aviation Administration proposes to amend part 39 of the Federal Aviation Regulations (14 CFR part 39) as follows:

PART 39—AIRWORTHINESS DIRECTIVES

1. The authority citation for part 39 continues to read as follows:

Authority: 49 U.S.C. 106(g), 40113, 44701.