Airworthiness Directives; Boeing Model 747-400, 777-200, and 777-300 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 747-400, 777-200, and 777-300 series airplanes. This proposal would require, for certain airplanes, replacement of the cell stack of the flight deck humidifier with a supplier-tested cell stack, or replacement with an end plate and subsequent deactivation of the flight deck humidifier. For other airplanes, this proposal would require replacement of the cell stack with a blanking plate or a new cell stack, or replacement of the blanking plate with a supplier-tested cell stack. This action is necessary to prevent an increased pressure drop across the humidifier and consequent reduced airflow to the flight deck, which could result in the inability to clear any smoke that might appear in the flight deck. This action is intended to address the identified unsafe condition.

DATES:

Comments must be received by November 3, 2003.

ADDRESSES:

Submit comments in triplicate to the Federal Aviation Administration (FAA), Transport Airplane Directorate, ANM-114, Attention: Rules Docket No. 2000-NM-360-AD, 1601 Lind Avenue, SW., Renton, Washington 98055-4056. Comments may be inspected at this location between 9 a.m. and 3 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-360-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 or 2000 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:

Jeffrey S. Palmer, Aerospace Engineer, Systems and Equipment Branch, ANM-130S, FAA, Seattle Aircraft Certification Office, 1601 Lind Avenue, SW., Renton, Washington 98055-4056; telephone (425) 917-6481; fax (425) 917-6590.

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 action 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 action must submit a self-addressed, stamped postcard on which the following statement is made: “Comments to Docket Number 2000-NM-360-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-360-AD, 1601 Lind Avenue, SW., Renton, Washington 98055-4056.

Discussion

The FAA has received reports of sagging cell stack membranes of the flight deck humidifiers on certain Boeing Model 747-400, 777-200, and 777-300 series airplanes. The sagging has been attributed to difficulties encountered during the membrane welding process. The result of the sagging membranes is an increased pressure drop across the humidifier (if it is activated), and consequent reduced airflow to the flight deck. These conditions, if not corrected, could result in the inability to clear any smoke that might appear in the flight deck.

Explanation of Relevant Service Information

We have reviewed and approved Boeing Alert Service Bulletin 747-21A2414, Revision 1, dated October 26, 2000 (for Model 747-400 series airplanes), and Boeing Service Bulletin 777-21A0048, Revision 1, dated September 7, 2000 (for Model 777-200 and 777-300 series airplanes). Service Bulletin 747-21A2414 describes procedures for replacement of the cell stack of the flight deck humidifier with a new or reworked cell stack, or replacement with an end plate and subsequent deactivation of the flight deck humidifier. Service Bulletin 777-21A0048 describes procedures for replacement of the cell stack with a blanking plate or a supplier-tested cell stack, or replacement of the blanking plate with a supplier-tested cell stack. Accomplishment of the actions specified in the service bulletins is intended to adequately address the identified unsafe condition.

Boeing Service Bulletins 747-21A2414 and 777-21A0048 refer to Hamilton Sundstrand Service Bulletins 821486-21-01 and 816086-21-01, respectively (both dated March 15, 2000), as additional sources of service information for replacement of the cell stack.

Boeing Service Bulletin 747-21A2414 also refers to Boeing Service Bulletin 747-21-2405, which provides information for activation and deactivation of the flight deck humidifier. Boeing Service Bulletin 777-21A0048 refers to Boeing Service Bulletin 777-21-0035, which provides information for activation of the flightdeck humidifier.

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 Boeing Service Bulletins 747-21A2414 and 777-21A0048, described previously, except as discussed below.

Differences Between Proposed AD and Service Bulletins

Boeing Service Bulletins 747-21A2414 and 777-21A0048 recommend replacing the cell stack within 60 days; the proposed AD would allow up to 90 days. In developing an appropriate compliance time, we considered the safety implications and operators' normal maintenance schedules for the timely replacement of the cell stack. Therefore, with manufacturer concurrence, we have determined that the proposed 90-day compliance time represents an appropriate interval to replace the cell stack and still maintain an adequate level of safety within the fleet.

Explanation of Certain Alternative Method of Compliance

Paragraph (c)(1) of this proposed AD would allow replacement of the cell stack with a blanking plate provided the humidifier system is deactivated. The service bulletin provides no procedures for deactivating the humidifier system. Therefore, this option must be done in accordance with a method approved by the FAA, or per data meeting the type certification basis of the airplane approved by a Boeing Company Designated Engineering Representative who has been authorized by the FAA to make such findings.

Cost Impact

There are approximately 35 airplanes of the affected design in the worldwide fleet. The FAA estimates that 12 airplanes of U.S. registry would be affected by this proposed AD. The FAA provides the following cost estimates, which would vary depending on the actions chosen by the operator, to comply with this proposed AD.

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.

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.