Airworthiness Directives; Boeing Model 747 Series Airplanes

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. 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 98-NM-282-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. 98-NM-282-AD, 1601 Lind Avenue, SW., Renton, Washington 98055-4056.

Discussion

The FAA has received reports indicating that fatigue cracking has been detected in the frame web and frame inner chord at stringer 26 at body station 1265. In addition, one report indicates that, on one airplane, the fuselage frame web and frame inner chord had severed above stringer 24 near the top of a frame inner chord reinforcement strap. This frame is the forward edge frame for main entry door number 3. Such fatigue cracking, if not detected and corrected in a timely manner, could result in rapid depressurization of the airplane.

Explanation of Relevant Service Information

The FAA has reviewed and approved Boeing Alert Service Bulletin 747-53A2416, Revision 1, dated May 6, 1999, which describes procedures for repetitive inspections to detect broken fasteners and cracking of the forward edge frame for main entry door number 3, and repair, if necessary. The inspection of the frames at the floor intercostal includes a detailed visual inspection for broken fasteners, an open hole high frequency eddy current (HFEC) inspection of certain fasteners in the frame inner chord to detect cracking, and a surface HFEC inspection of the frame web to detect cracking. For certain airplanes, the service bulletin recommends a surface HFEC inspection and an open hole HFEC inspection of the frames at the top of the inner chord reinforcement strap to detect cracking. Accomplishment of the actions specified in the alert service bulletin 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 alert service bulletin described previously, except as discussed below.

Differences Between Alert Service Bulletin and This AD

Operators should note that, although the alert service bulletin specifies that the manufacturer may be contacted for repair data for cracking conditions, this AD requires the repair of those conditions to be accomplished in accordance with a method approved by the FAA, or in accordance with 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. The alert service bulletin also indicates that a modification to the frame and lateral intercostal can be made that will increase the interval between frame inspections, and that the procedures for such a modification will be included in a subsequent revision to the alert service bulletin. Any modification incorporated to increase the interval between inspections or as terminating action for the inspections must be approved as an alternative method of compliance in accordance with paragraph (d) of this AD.

Cost Impact

There are approximately 1,182 airplanes of the affected design in the worldwide fleet. The FAA estimates that 251 airplanes of U.S. registry would be affected by this proposed AD. It would take approximately 1 work hour per airplane to accomplish the proposed inspection of the frames at the floor intercostal, at an average labor rate of $60 per work hour. Based on these figures, the cost impact of this proposed inspection on U.S. operators is estimated to be $15,060, or $60 per airplane, per inspection cycle. The FAA estimates that the proposed inspection of the frames at the top of the inner chord reinforcement strap would be required to be accomplished on 103 U.S.-registered airplanes. It would take approximately 1 work hour per airplane to accomplish the proposed inspection, at an average labor rate of $60 per work hour. Based on these figures, the cost impact of this proposed inspection on U.S. operators is estimated to be $6,180, or $60 per airplane, per inspection cycle. 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 AD were not adopted.

Regulatory Impact

The regulations proposed herein would 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 proposal would not have sufficient federalism implications to warrant the preparation of a Federalism Assessment. 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.

Sec. 39.13 [Amended]

2. Section 39.13 is amended by adding the following new airworthiness directive:

Boeing: Docket 98-NM-282-AD. Applicability: Model 747 series airplanes, as listed in Boeing Alert Service Bulletin 747-53A2416, Revision 1, dated May 6, 1999; certificated in any category.

Note 1: This AD applies to airplanes that have been converted from a passenger configuration to a special freighter configuration.

Note 2: This AD applies to each airplane identified in the preceding applicability provision, regardless of whether it has been

modified, altered, or repaired in the area subject to the requirements of this AD. For airplanes that have been modified, altered, or repaired so that the performance of the requirements of this AD is affected, the owner/operator must request approval for an alternative method of compliance in accordance with paragraph (d) of this AD. The request should include an assessment of the effect of the modification, alteration, or repair on the unsafe condition addressed by this AD; and, if the unsafe condition has not been eliminated, the request should include specific proposed actions to address it.

Compliance: Required as indicated, unless accomplished previously. To detect and correct cracking of the inner chord and web of the body station 1265 edge frame between stringers 23 and 27, which could result in rapid depressurization of the airplane, accomplish the following:

Inspections

(a) Accomplish the flight safety inspections of the frames at the floor intercostal to detect broken fasteners and cracking, in accordance with Figure 5 of Boeing Alert Service Bulletin 747- 53A2416, Revision 1, dated May 6, 1999, at the applicable time specified in paragraph (a)(1), (a)(2), or (a)(3) of this AD. Repeat the inspection thereafter at intervals not to exceed 3,000 flight cycles.

Note 3: Figure 5 of the alert service bulletin includes a detailed visual inspection for broken fasteners, an open hole high frequency eddy current (HFEC) inspection of certain fasteners in the frame inner chord to detect cracking, and a surface HFEC inspection of the frame web to detect cracking.

Note 4: For the purposes of this AD, a detailed visual inspection is defined as: ``An intensive visual examination of a specific structural area, system, installation, or assembly to detect damage, failure, or irregularity. Available lighting is normally supplemented with a direct source of good lighting at intensity deemed appropriate by the inspector. Inspection aids such as mirror, magnifying lenses, etc., may be used. Surface cleaning and elaborate access procedures may be required.''

Note 5: The alert service bulletin gives instructions to perform an open hole inspection, but does not give instructions to oversize the fastener hole after the inspection. This will keep sufficient material to oversize the hole at a later date when the modification work is accomplished.

(1) For airplanes that have accumulated fewer than 10,000 total flight cycles as of the effective date of this AD: Inspect prior to the accumulation of 10,000 total flight cycles, or within 1,000 flight cycles after the effective date of this AD, whichever occurs later. (2) For airplanes that have accumulated between 10,000 and 20,000 total flight cycles as of the effective date of this AD: Inspect prior to the accumulation of 11,000 total flight cycles, or within 750 flight cycles after the effective date of this AD, whichever occurs later. (3) For airplanes that have accumulated more than 20,000 total flight cycles as of the effective date of this AD: Inspect prior to the accumulation of 20,750 total flight cycles, or within 500 flight cycles after the effective date of this AD, whichever occurs later. (b) For Group 1 airplanes, as identified in Boeing Alert Service Bulletin 747-53A2416, Revision 1, dated May 6, 1999, on which the extended chord reinforcement strap modification specified in Boeing Service Bulletin 747-53-2066, dated June 28, 1972, has not been accomplished or on which the extended chord reinforcement strap modification was accomplished after the accumulation of 10,000 total flight cycles: Accomplish the surface HFEC inspection and the open hole HFEC inspection, as applicable, of the frames at the top of the inner chord reinforcement strap to detect cracking, in accordance with Figure 6 of the alert service bulletin at the applicable time specified in either paragraph (b)(1) or (b)(2) of this AD. Repeat the inspection thereafter at intervals not to exceed 800 flight cycles. (1) For airplanes that have accumulated 20,000 total flight cycles or fewer as of the effective date of this AD: Inspect prior to the accumulation of 16,000 total flight cycles, or within 500 flight cycles after the effective date of this AD, whichever occurs later. (2) For airplanes that have accumulated more than 20,000 total flight cycles as of the effective date of this AD: Inspect prior to the accumulation of 20,500 total flight cycles, or within 250 flight cycles after the effective date of this AD, whichever occurs later.

Repair

(c) If any broken fastener or cracking is detected during the inspections required by paragraph (a) or (b) of this AD, prior to further flight, repair in accordance with a method approved by the Manager, Seattle Aircraft Certification Office (ACO), FAA, Transport Airplane Directorate; or in accordance with data meeting the type certification basis of the airplane approved by a Boeing Company Designated Engineering Representative who has been authorized by the Manager, Seattle ACO, to make such findings. For a repair method to be approved by the Manager, Seattle ACO, as required by this paragraph, the Manager's approval letter must specifically reference this AD.

Alternative Methods of Compliance

(d) An alternative method of compliance or adjustment of the compliance time that provides an acceptable level of safety may be used if approved by the Manager, Seattle ACO. Operators shall submit their requests through an appropriate FAA Principal Maintenance Inspector, who may add comments and then send it to the Manager, Seattle ACO.

Note 6: Information concerning the existence of approved alternative methods of compliance with this AD, if any, may be obtained from the Seattle ACO.

Special Flight Permits

(e) Special flight permits may be issued in accordance with Secs. 21.197 and 21.199 of the Federal Aviation Regulations (14 CFR 21.197 and 21.199) to operate the airplane to a location where the requirements of this AD can be accomplished.

Issued in Renton, Washington, on August 16, 1999. D. L. Riggin, Acting Manager, Transport Airplane Directorate, Aircraft Certification Service. [FR Doc. 99-21693 Filed 8-19-99; 8:45 am] BILLING CODE 4910-13-P