Airworthiness Directives; Boeing Model 757 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 757 series airplanes. This proposal would require repetitive detailed inspections of the support brackets and associated fasteners for the hydraulic lines located in the nacelle struts, and related investigative and corrective actions as necessary. This proposal also provides an optional terminating action for the repetitive inspections. This action is necessary to prevent flammable fluids from leaking into the interior compartment of the nacelle struts where ignition sources exist, which could result in the ignition of flammable fluids and an uncontained fire. This action is intended to address the identified unsafe condition.

DATES:

Comments must be received by July 1, 2004.

ADDRESSES:

Submit comments in triplicate to the Federal Aviation Administration (FAA), Transport Airplane Directorate, ANM-114, Attention: Rules Docket No. 2003-NM-252-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. 2003-NM-252-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 Airplanes, 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:

Tom Thorson, Aerospace Engineer, Propulsion Branch, ANM-140S, FAA, Seattle Aircraft Certification Office, 1601 Lind Avenue, SW., Renton, Washington 98055-4056; telephone (425) 917-6508; 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 2003-NM-252-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. 2003-NM-252-AD, 1601 Lind Avenue, SW., Renton, Washington 98055-4056.

Discussion

The FAA has received reports of failure of the support brackets and associated fasteners for the hydraulic lines located in the nacelle struts. These failures occurred on certain Model 757 series airplanes equipped with Rolls-Royce engines. The hydraulic lines provide supply pressure from the hydraulic pumps to the airframe and are subject to high frequency pressure oscillations/vibrations. Investigation by the manufacturer revealed that the operating pressure and surge loads from the hydraulic pumps are higher than originally expected and exceed the capability of the design for the support bracket structure.

The hydraulic lines are located in the upper fairing compartment of the nacelle struts. The upper fairing compartment is a flammable leakage zone and is isolated from other strut compartments by a protective vapor barrier. The vapor barrier acts as a seal to keep flammable fluids and vapors from hydraulic and fuel line leaks out of the interior portion of the strut where pneumatic bleed air ducts are located. The surface temperature of the bleed air ducts is hot enough to be an ignition source. The reported condition of sheared or loose fasteners, or damage to the strut webs adjacent to the support brackets and associated fasteners, compromises the vapor barrier, which allows flammable fluids to leak into the interior compartments of the nacelle struts. Such a condition, if not corrected, could result in ignition of flammable fluids and an uncontained fire.

Explanation of Relevant Service Information

The FAA has reviewed and approved Boeing Alert Service Bulletins 757-54A0045 (for Model 757-200 series airplanes), dated May 22, 2003; and 757-54A0046 (for Model 757-300 series airplanes), dated May 29, 2003. These service bulletins describe procedures for inspecting the support brackets and associated fasteners for the hydraulic lines located in the nacelle struts for loose and/or damaged parts, and related investigative and corrective actions. Evidence of damage includes sheared fasteners and/or elongated fastener holes in the strut webs. If no damaged or loose parts are found, the service bulletins state that operators may either repeat the inspection of the hydraulic line support brackets and associated fasteners at the intervals specified in the service bulletin, or do the related investigative and corrective actions.

The procedures for the related investigative and corrective actions include:

• Inspecting the fuel and hydraulic lines and strut webs for evidence of damage (e.g., chafing or holes) caused by a loose support bracket and/or line.
• Replacing or repairing damaged fuel lines.
• Replacing damaged hydraulic lines.
• Repairing damaged areas of the strut webs.
• Contacting Boeing for damage that is beyond the repair limitations specified in the structural repair manual.
• Modifying the support brackets by installing additional straps and stronger fasteners.

Accomplishment of the actions specified in the service bulletins is intended to adequately address the identified unsafe condition.

Explanation of Requirements of Proposed AD

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 service bulletins described previously, except as discussed below. This proposed AD also would provide for optional terminating action for the repetitive inspections.

Difference Between the Service Bulletins and Proposed AD

Although the service bulletins specify that operators may contact the manufacturer for disposition of certain repair conditions, this proposed AD would require operators to repair those conditions per a method approved by the FAA.

Cost Impact

There are approximately 603 airplanes of the affected design in the worldwide fleet. The FAA estimates that 325 airplanes of U.S. registry would be affected by this proposed AD, that it would take approximately 22 work hours per airplane to accomplish the proposed inspections, and that the average labor rate is $65 per work hour. Based on these figures, the cost impact of the proposed AD on U.S. operators is estimated to be $464,750, or $1,430 per airplane.

The cost impact figure discussed above is 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.