Airworthiness Directive · Amendment 39-11582 · Boeing Model 747-100, -200, and 747SP Series Airplanes
Boeing Model 747-100, -200, and 747SP Series Airplanes
Model 747-100, -200, and 747SP series airplanes; line numbers 1 through 567 inclusive; equipped with aluminum diagonal brace underwing fittings; certificated in any category.
Note 1: 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 (f) 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.
This amendment adopts a new airworthiness directive (AD), applicable to certain Boeing Model 747-100, -200, and 747SP series airplanes, that requires repetitive detailed visual and ultrasonic inspections to detect missing, damaged, or broken taperlock bolts in the diagonal brace underwing fittings; and corrective actions, if necessary. This AD also requires eventual replacement of the aft 10 taperlock bolts with new bolts, which constitutes terminating action for the repetitive inspections. This amendment is prompted by reports of damaged, broken, and corroded taperlock bolts of the diagonal brace underwing fittings on the outboard strut due to stress corrosion cracking. The actions specified by this AD are intended to prevent loss of the underwing fitting load path due to missing, damaged, or broken taperlock bolts, which could result in separation of the engine and strut from the airplane.
To prevent loss of the underwing fitting load path due to missing, damaged, or broken taperlock bolts, which could result in separation of the engine and strut from the airplane, accomplish the following:
(a) Prior to the accumulation of 9,000 total flight cycles, or within 18 months after the effective date of this AD, whichever occurs later, accomplish the actions required by paragraphs (a)(1) and (a)(2) of this AD in accordance with Boeing Alert Service Bulletin 747-57A2308, dated August 6, 1998. Thereafter, repeat the inspections at intervals not to exceed 18 months until accomplishment of the actions specified in paragraph (d) of this AD.
(1) Perform a detailed visual inspection to detect missing taperlock bolts in the diagonal brace underwing fitting at the Number 1 and Number 4 pylons.
Note 2: 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.”
(2) Perform an ultrasonic inspection to detect damaged or broken taperlock bolts in the diagonal brace underwing fitting at the Number 1 and Number 4 pylons.
(b) If any missing, damaged, or broken taperlock bolt is detected during any inspection required by paragraph (a) of this AD, prior to further flight, perform the applicable corrective actions (i.e., inspection, drill/ream, and replacement) in accordance with Boeing Alert Service Bulletin 747-57A2308, dated August 6, 1998; except as provided in paragraph (c) of this AD. Replacement of any taperlock bolt with a new bolt in accordance with this paragraph constitutes terminating action for the repetitive inspections required by paragraph (a) of this AD for that bolt only.
(c) If any crack is detected during the inspection required by paragraph (b) of this AD and the damage to a bolt hole exceeds first oversize (for 0.5-inch bolts) or second oversize (for 0.4375-inch bolts); and the service bulletin specifies to contact Boeing for appropriate action: 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 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.
(d) Within 48 months after the effective date of this AD, accomplish the actions required by paragraphs (d)(1) and (d)(2) of this AD in accordance with Boeing Alert Service Bulletin 747-57A2308, dated August 6, 1998. Accomplishment of the actions specified in this paragraph constitutes terminating action for the repetitive inspection requirements of this AD.
(1) Prior to accomplishing the replacement required by paragraph (d)(2) of this AD, perform an open hole high frequency eddy current inspection to detect cracks at the bolt hole locations of the aft 10 taperlock bolts. If any cracking is detected, prior to further flight, perform applicable corrective actions in accordance with paragraph (c) of this AD.
(2) Replace the aft 10 taperlock bolts with new bolts in the diagonal brace underwing fitting at the Number 1 and Number 4 pylons.
Note 3: Accomplishment of the replacement of the diagonal brace underwing fitting in accordance with Figures 5 through 9 of Boeing Service Bulletin 747-57-2288, Revision 1, dated June 26, 1997; or the clearance adjustment in accordance with Figures 10 through 14 of that service bulletin; is acceptable for compliance with the requirements of paragraph (d) of this AD.
(e) As of the effective date of this AD, no person shall install a bolt, part number BACB30PE() * (), or any other bolt made of 4340, 8740, or PH13-8 Mo steel, in the locations specified in this AD, on any airplane listed in the applicability of this AD.
