AD 96-03-01

Effective February 16, 1996.

The incorporation by reference of certain publications listed in the regulations is approved by the Director of the Federal Register as of February 16, 1996.

Comments for inclusion in the Rules Docket must be received on or before April 1, 1996.

Submit comments in triplicate to the Federal Aviation Administration (FAA), Transport Airplane Directorate, ANM-103, Attention: Rules Docket No. 95-NM-276-AD, 1601 Lind Avenue, SW., Renton, Washington 98055-4056.

The service information referenced in this AD 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; or at the Office of the Federal Register, 800 North Capitol Street, NW., suite 700, Washington, DC.

Tammy L. Dow, Aerospace Engineer, Airframe Branch, ANM-120S, FAA, Seattle Aircraft Certification Office, 1601 Lind Avenue SW., Renton, Washington; telephone (206) 227-2771; fax (206) 227-1181.

Recently, the FAA received reports indicating that the upper bolt and nut of the tangential link of the aft engine on Model 747 airplanes were found to have migrated out of proper position. In three cases, the bolt had completely backed out of the hole. Analysis conducted by the manufacturer demonstrated that the nuts used to secure the bolts may not provide adequate run-on torque. Additionally, there was evidence that lubricants were used on the threads of some of the bolts. These conditions can allow the nut to rotate and disengage from the bolt. With no nut or other retention for the bolt, normal vibration causes the bolt to loosen and migrate out of the tangential link. Loss of the bolt would reduce the capability of the engine retention system, and could result in cracking of the engine turbine exhaust case due to the increased load. This condition, if not corrected, could result in separation of the engine from the airplane.

The FAA has reviewed and approved Boeing Alert Service Bulletin 747-71A2277, dated November 29, 1995, which describes procedures for repetitive inspections of the lower engine mount to verify if the tangential link upper bolt nut is properly oriented and to verify that the tangential link upper bolt nut is torqued within certain limits. Additionally, the service bulletin describes procedures for the replacement of the bolt and nut with serviceable parts, if necessary. The alert service bulletin also describes certain other follow-on procedures for airplanes on which the tangential link upper bolt is missing. Those procedures involve a visual inspection to detect damage and deformation of the lower engine mount lugs that attach the affected safety link; magnetic particle inspections to detect cracking of the lower engine mount lugs; detail visual inspections to detect cracking, bulging, discoloration, and corrosion of the engine mounts and adjacent structures; and replacement of the lower engine mount fittings with serviceable parts, if necessary; installation of new safety links, bolts, and nuts; and installation of the tangential link upper bolt.

The FAA also has reviewed and approved Boeing Service Bulletin 747-71-2206, Revision 1, dated November 12, 1987 (as revised by Boeing 747 Notice of Status Change No. 747-71-2206 NSC 1, dated December 4, 1987, and Boeing 747 Notice of Status Change No. 747-71-2206 NSC 2, dated March 17, 1988). This service information describes procedures for replacement of the safety links with modified safety links. Accomplishment of this replacement eliminates the need for repetitive inspections of lower engine mount bolt and nut.

Since an unsafe condition has been identified that is likely to exist or develop on other Boeing Model 747 series airplanes of the same type design, this AD is being issued to prevent possible separation of the engine from the airplane due to consequences associated with the complete migration of the tangential link upper bolt. This action requires repetitive visual inspections to verify if the tangential link upper bolt is correctly oriented; inspections to determine if the tangential link upper bolt nut is torqued within certain limits; and replacement of the bolt and nut with serviceable parts, if necessary. This action also requires certain other follow-on procedures for airplanes on which the tangential link upper bolt is missing. Additionally, this AD provides for replacement of the safety links as optional terminating action for the repetitive inspection requirements. The actions are required to be accomplished in accordance with the service bulletins described previously.

Since a situation exists that requires the immediate adoption of this regulation, it is found that notice and opportunity for prior public comment hereon are impracticable, and that good cause exists for making this amendment effective in less than 30 days.

This is considered to be interim action. Once final action is identified, the FAA may consider further rulemaking.

Although this action is in the form of a final rule that involves requirements affecting flight safety and, thus, was not preceded by notice and an opportunity for public comment, comments are invited on this rule. Interested persons are invited to comment on this 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 under the caption ADDRESSES. All communications received on or before the closing date for comments will be considered, and this rule may be amended in light of the comments received. Factual information that supports the commenter's ideas and suggestions is extremely helpful in evaluating the effectiveness of the AD action and determining whether additional rulemaking action would be needed.

Comments are specifically invited on the overall regulatory, economic, environmental, and energy aspects of the rule that might suggest a need to modify the 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 that summarizes each FAA-public contact concerned with the substance of this AD will be filed in the Rules Docket.

Commenters wishing the FAA to acknowledge receipt of their comments submitted in response to this rule must submit a self-addressed, stamped postcard on which the following statement is made: ``Comments to Docket Number 95-NM-276-AD.'' The postcard will be date stamped and returned to the commenter.

The regulations adopted herein will not have substantial direct effects 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, in accordance with Executive Order 12612, it is determined that this final rule does not have sufficient federalism implications to warrant the preparation of a Federalism Assessment.

The FAA has determined that this regulation is an emergency regulation that must be issued immediately to correct an unsafe condition in aircraft, and that it is not a ``significant regulatory action'' under Executive Order 12866. It has been determined further that this action involves an emergency regulation under DOT Regulatory Policies and Procedures (44 FR 11034, February 26, 1979). If it is determined that this emergency regulation otherwise would be significant under DOT Regulatory Policies and Procedures, a final regulatory evaluation will be prepared and placed in the Rules Docket. A copy of it, if filed, may be obtained from the Rules Docket at the location provided under the caption ADDRESSES.

Air transportation, Aircraft, Aviation safety, Incorporation by reference, Safety.

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

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

Authority: 49 USC 106(g), 40113, 44701.