AD 96-26-51

January 13, 1997, to all persons except those persons to whom it was made immediately effective by telegraphic AD T96-26-51, issued on December 13, 1996, which contained the requirements of this amendment.

Comments for inclusion in the Rules Docket must be received on or before March 10, 1997.

Submit comments in triplicate to the Federal Aviation Administration (FAA), Transport Airplane Directorate, ANM-103, Attention: Rules Docket No. 96-NM-276-AD, 1601 Lind Avenue, SW., Renton, Washington 98055-4056.

Information concerning this AD may be obtained from or examined at the FAA, Transport Airplane Directorate, 1601 Lind Avenue, SW., Renton, Washington.

Tamara Dow, Aerospace Engineer, Airframe Branch, ANM-120S, FAA, Transport Airplane Directorate, Seattle Aircraft Certification Office, 1601 Lind Avenue, SW., Renton, Washington 98055-4056; telephone (206) 227-2771; fax (206) 227-1181.

On December 13, 1996, the FAA issued telegraphic AD T96-26-51, which is applicable to certain Boeing Model 747 series airplanes powered by Rolls Royce Model RB211 series engines.

That action was prompted by two reports of cracking of the aft torque bulkhead at the number 1 and number 2 engine pylons. This cracking occurred on a Boeing Model 747-200F series airplane powered by Rolls Royce Model RB211 series engines. The airplane had accumulated 69,506 total flight hours and 17,499 total flight cycles.

Investigation revealed that the aft torque bulkhead at the number 1 pylon was cracked completely through just above the lower spar fitting where the fitting attaches to the diagonal brace. The crack extended eight inches forward on the outboard side skin of the number 1 pylon. In addition, the lower portion of the aft torque bulkhead at the number 1 pylon had separated and had dropped down approximately 0.5 inch.

Investigation also revealed that the aft torque bulkhead at the number 2 pylon was cracked (1.2 inch) in approximately the same location as the cracking on the number 1 pylon.

The cause of this cracking is unknown at this time. Modification of the strut/wing, which is currently required by AD 95-13-05, amendment 39-9285 (60 FR 33333, June 28, 1995), had not yet been accomplished on the airplane at the time of discovery of the cracking. However, it also is not known if this modification would have prevented this condition.

Cracking of the aft torque bulkhead at the engine pylons, if not detected and corrected in a timely manner, could result in failure of a pylon and consequent separation of the engine from the wing.

The FAA has determined that a one-time inspection to detect cracks and corrosion of the aft torque bulkhead at all four engine pylons is necessary to address the identified unsafe condition in a timely manner.

Since the unsafe condition described is likely to exist or develop on other airplanes of the same type design, the FAA issued telegraphic AD T96-26-51 to require a one-time detailed visual inspection to detect cracks and corrosion in the following areas: (1) The external surface of the lower half of the aft torque bulkhead at all four engine pylons, and (2) the external surface of the inboard and outboard side skins for a distance of 36 inches forward of the plane of the aft torque bulkhead at all four engine pylons. The AD also requires repair of any cracked or corroded engine pylon. In addition, the AD requires that operators submit a report of all inspection findings to the FAA.

Since it was found that immediate corrective action was required, notice and opportunity for prior public comment thereon were impracticable and contrary to the public interest, and good cause existed to make the AD effective immediately by individual telegrams issued on December 13, 1996, to all known U.S. owners and operators of certain Boeing Model 747 series airplanes powered by Rolls Royce Model RB211 series engines. These conditions still exist, and the AD is hereby published in the Federal Register as an amendment to section 39.13 of the Federal Aviation Regulations (14 CFR 39.13) to make it effective to all persons.

This is considered to be interim action. The reports of inspection results that are required by this AD will enable the FAA to obtain better insight into the nature, cause, and extent of cracking found at the number 1 and number 2 engine pylons, and eventually to develop final action to address the subject unsafe condition. Once final action has been 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 96-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, 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 U.S.C. 106(g), 40113, 44701.