Airworthiness Directive · Amendment 39-11797 · Boeing Model 747 Series Airplanes
Boeing Model 747 Series Airplanes
Model 747 series airplanes, as listed in Boeing Alert Service Bulletin 747-53A2425, dated October 29, 1998; 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 (g) 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 series airplanes, that requires repetitive inspections of the aft pressure bulkhead to detect cracking, and repair, if necessary. This amendment is prompted by a report of fatigue cracking found in the upper half of the aft pressure bulkhead. The actions specified by this AD are intended to detect and correct cracking in the aft pressure bulkhead, which could result in rapid decompression of the fuselage or overpressurization of the tail section.
To detect and correct cracking in the aft pressure bulkhead, which could result in rapid decompression of the fuselage or overpressurization of the tail section, accomplish the following:
(a) Except as provided by paragraph (f) of this AD, prior to the accumulation of 20,000 total flight cycles, or within 12 months after the effective date of this AD, whichever occurs later, perform a detailed visual inspection of the upper half of the aft pressure bulkhead to detect cracking, in accordance with Figure 6 or 7, as applicable, of Boeing Alert Service Bulletin 747-53A2425, dated October 29, 1998. Repeat the detailed visual inspection thereafter at intervals not to exceed 1,500 flight cycles. For areas of the upper half of the aft pressure bulkhead that have been repaired previously, this detailed visual inspection may be deferred for up to 15,000 flight cycles after accomplishment of the repair, as described in the NOTE in paragraph 3.D. of the Accomplishment Instructions of the alert service bulletin.
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.”
(b) Except as provided by paragraph (f) of this AD, if no cracking is detected during the initial detailed visual inspection required by paragraph (a) of this AD: Within 1,500 flight cycles after accomplishment of that inspection, perform a high frequency eddy current (HFEC) inspection of the upper and lower halves of the aft pressure bulkhead to detect cracking, in accordance with Figure 8 of Boeing Alert Service Bulletin 747-53A2425, dated October 29, 1998. Repeat the HFEC inspection thereafter at intervals not to exceed 3,000 flight cycles.
(c) Except as provided by paragraph (f) of this AD, if any cracking is detected during any inspection required by paragraph (a) of this AD: Prior to further flight, perform an HFEC inspection of the upper and lower halves of the aft pressure bulkhead to detect cracking, in accordance with Figure 8 or 9, as applicable, of Boeing Alert Service Bulletin 747-53A2425, dated October 29, 1998. Repeat the HFEC inspection thereafter at intervals not to exceed 3,000 flight cycles.
(d) Except as provided by paragraphs (e) and (f) of this AD, if any cracking is detected during any inspection required by paragraph (a), (b), or (c) of this AD: Prior to further flight, repair in accordance with Boeing Alert Service Bulletin 747-53A2425, dated October 29, 1998.
(e) If any cracking is detected during any inspection required by paragraph (a), (b), or (c) of this AD, and Boeing Alert Service Bulletin 747-53A2425, dated October 29, 1998, specifies to contact Boeing for repair instructions: Repair any cracking, prior to further flight, 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 (DER) 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 approval letter must specifically reference this AD.
(f) Where Boeing Alert Service Bulletin 747-53A2425, dated October 29, 1998, specifies that an inspection or a repair, as applicable, may be accomplished in accordance with an operator's “equivalent procedure”: The inspection or repair, as applicable, must be accomplished in accordance with the applicable chapter of the Boeing 747 Maintenance Manual or the Boeing 747 Structural Repair Manual specified in the alert service bulletin.
