AD 94-10-05

94-10-05 BOEING: Amendment 39-8912. Docket 94-NM-59-AD.

Applicability: Model 747 series airplanes; equipped with Pratt & Whitney JT9D-3 and -7 series engines (does not apply to -70 series engines); certificated in any category.

Compliance: Required as indicated, unless accomplished previously.

To prevent complete migration of the forward lower engine mount bolt out of the joint, which could result in the separation of the engine from the strut, accomplish the following:

(a) For all applicable airplanes: Within 60 days after the effective date of this AD, visually inspect the forward lower engine mount for migration of the forward lower engine mount bolts, both transverse and forward-aft, in accordance with Boeing Alert Service Bulletin 747-71A2269, dated April 14, 1994 (hereafter referred to as "the service bulletin"). The maximum gap for the transverse bolt and the forward-aft bolt in the joint is 0.06 inch; a bolt is considered to have migrated if the gap exceeds this value. Prior to further flight, accomplish the requirements of either paragraph (b) or (c) of this AD, as applicable.

(b) For airplanes not equipped with a steel retention bracket installed in accordance with Boeing Service Bulletin 747-71-2192 or its production equivalent, accomplish the following:

(1) If the inspection required by paragraph (a) of this AD indicates that the bolt has not migrated, accomplish paragraphs (b)(1)(i) and (b)(1)(ii) of this AD:

(i) Prior to further flight, perform a torque check of the nut in accordance with the service bulletin. If the torque is outside of the range specified in the service bulletin, prior to further flight, replace the nut with a new nut having part number NAS1805 and associated washer.

(ii) Repeat the inspection for migration of bolts with nuts having part number BACN10JC at intervals not to exceed 2,100 flight hours. Repeat the inspection for migration of bolts with nuts having part number NAS1805 at intervals not to exceed 3,200 flight hours.

(2) If the inspection required by paragraph (a) of this AD indicates that the bolt has migrated, accomplish paragraph (b)(2)(i) of this AD, and either paragraph (b)(2)(ii) or paragraph (b)(2)(iii), as applicable:

(i) Prior to further flight, remove the nut and replace it with a new nut having part number NAS1805 and associated washer, in accordance with the service bulletin. Thereafter, repeat the inspection for migration of these bolts at intervals not to exceed 3,200 flight hours.

(ii) Except as provided by paragraph (b)(2)(iii) of this AD: Prior to further flight, remove the bolt and visually inspect it for damage, in accordance with Part V of the service bulletin; and visually inspect the bolt bushings for damage, in accordance with Part III of the service bulletin. If the bolt is damaged, prior to further flight, replace the bolt with a new bolt having the same part number. If the bushings are damaged, prior to furtherflight, replace the bushings.

(iii) The inspections of the bolt and bolt bushings required by paragraph (b)(2)(ii) of this AD may be deferred for a maximum of 3,200 flight hours, provided that all of the following apply:

(A) The bolt is visually inspected for thread damage as described in Part IV of the service bulletin and no damage is found; and

(B) The nut threads are still fully engaged with the bolt; and

(C) The migrated bolt has not contacted adjacent structure or systems; and

(D) The bolt is repositioned back to clamp-up position, as described in Part IV of the service bulletin.

(c) For airplanes equipped with a steel retention bracket installed in accordance with Boeing Service Bulletin 747-71-2192 or its production equivalent, accomplish the following:

(1) If the inspection required by paragraph (a) of this AD indicates that the bolt has not migrated, accomplish paragraphs (c)(1)(i) and (c)(1)(ii) of this AD:

(i) Prior to further flight, ensure that the washer on the nut side does not rotate freely. If the washer rotates freely, prior to further flight, replace the nut with a new nut having part number NAS1805 and associated washer.

(ii) Repeat the inspection for migration of bolts with nuts having part number BACN10JC at intervals not to exceed 3,200 flight hours. Repeat the inspection for migration of bolts with nuts having part number NAS1805 at intervals not to exceed 6,000 flight hours.

(2) If the inspection required by paragraph (a) of this AD indicates that the bolt has migrated, accomplish paragraph (c)(2)(i) of this AD, and either paragraph (c)(2)(ii) or paragraph (c)(2)(iii), as applicable:

(i) Prior to further flight, remove the nut and replace it with a new nut having part number NAS1805 and associated washer, in accordance with the service bulletin. Thereafter, repeat the inspection for migration of these bolts at intervals not to exceed 6,000 flight hours.

(ii) Exceptas provided by paragraph (c)(2)(iii) of this AD: Prior to further flight, remove the bolt and visually inspect it for damage, in accordance with Part V of the service bulletin; and visually inspect the bolt bushings for damage, in accordance with Part III of the service bulletin. If the bolt is damaged, prior to further flight, replace the bolt with a new bolt having the same part number. If the bushings are damaged, prior to further flight, replace the bushings.

(iii) The inspections of the bolt and bolt bushings required by paragraph (c)(2)(ii) of this AD may be deferred for a maximum of 3,200 flight hours, provided that all of the following apply:

(A) The bolt is visually inspected for thread damage, as described in Part IV of the service bulletin, and no damage is found; and

(B) The nut threads are still fully engaged with the bolt; and

(C) The migrated bolt has not contacted adjacent structure or systems; and

(D) The bolt is repositioned backto clamp-up position, as described in Part IV of the service bulletin.

(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 Aircraft Certification Office (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: Information concerning the existence of approved alternative methods of compliance with this AD, if any, may be obtained from the Seattle ACO.

(e) Special flight permits may be issued in accordance with sections 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.

(f) The actions shall be done in accordance with Boeing Alert Service Bulletin 747-71A2269, dated April 14, 1994. This incorporation by reference was approved by the Director of the Federal Register in accordance with 5 U.S.C. 552(a) and 1 CFR Part 51. Copies may be obtained from Boeing Commercial Airplane Group, P.O. Box 3707, Seattle, Washington 98124-2207. Copies may be inspected 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.

(g) This amendment becomes effective on May 31, 1994.