Airworthiness Directive · Amendment 39-11880 · Boeing Model 747 and 767 Series Airplanes Equipped With General Electric CF6-80C2 Series Engines
Boeing Model 747 and 767 Series Airplanes Equipped With General Electric CF6-80C2 Series Engines
Model 747 and 767 series airplanes equipped with General Electric CF6-80C2 series engines, 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 (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.
This amendment adopts a new airworthiness directive (AD), applicable to certain Boeing Model 747 and 767 series airplanes, that requires repetitive functional tests of the directional pilot valve (DPV) of the thrust reversers to detect pneumatic leakage, and corrective action, if necessary. This amendment is prompted by a report of a latent failure mode of the fail-safe features of the thrust reverser system identified as possible leakage of the DPV that is due to a poppet being jammed slightly open or a leaking o-ring. The actions specified by this AD are intended to ensure the integrity of the fail- safe features of the thrust reverser system by preventing possible failure modes, which could result in inadvertent deployment of a thrust reverser during flight, and consequent reduced controllability of the airplane.
To ensure the integrity of the fail-safe features of the thrust reverser system by preventing possible failure modes, which could result in inadvertent deployment of a thrust reverser during flight, and consequent reduced controllability of the airplane, accomplish the following:
(a) For Model 747 and 767 series airplanes equipped with thrust reversers that HAVE NOT been modified in accordance with Boeing Service Bulletin 747-78-2151 or 767-78-0063, as applicable, or a production equivalent: Within 60 days after the effective date of this AD, perform a functional test of the directional pilot valve (DPV) of the thrust reversers to detect pneumatic leakage in accordance with Boeing Alert Service Bulletin 747-78A2170, or Boeing Service Bulletin 767-78-0084, as applicable, both dated October 21, 1999. Repeat the functional test thereafter at intervals not to exceed 1,000 flight hours.
(b) For Model 747 and 767 series airplanes equipped with thrust reversers that have been modified in accordance with Boeing Service Bulletin 747-78-2151 or 767-78-0063, as applicable, or a production equivalent: Within 180 days after the effective date of this AD, perform a functional test of the DPV of the thrust reversers to detect pneumatic leakage in accordance with Boeing Alert Service Bulletin 747-78A2170, or Boeing Service Bulletin 767-78-0084, as applicable, both dated October 21, 1999. Repeat the functional test thereafter at intervals not to exceed 6,000 flight hours.
Note 2: For airplanes modified during production: Functional tests accomplished in accordance with a production equivalent are acceptable for the initial functional test required by paragraph (b) of this AD.
(c) If any functional test required by paragraph (a) or (b) of this AD cannot be successfully performed as specified in Boeing Alert Service Bulletin 747-78A2170, or Boeing Service Bulletin 767-78-0084, as applicable, both dated October 21, 1999; or if any discrepancy is detected during any functional test required by paragraph (a) or (b) of this AD: Prior to further flight, correct the discrepancy in accordance with the procedures specified in the applicable Boeing Model 747 or 767 Airplane Maintenance Manual. Additionally, prior to further flight, any failed functional test required by paragraph (a) or (b) of this AD must be repeated and successfully accomplished. Repeat the functional test thereafter at the intervals required by paragraph (a) or (b) of this AD, as applicable.
