Airworthiness Directive · Amendment 39-11932 · Boeing Model 747-400 Series Airplanes
Boeing Model 747-400 Series Airplanes
Model 747-400 series airplanes, having line numbers 696 through 1187 inclusive, certificated in any category; equipped with Honeywell inertial reference units (IRU).
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 (c) 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 747-400 series airplanes, that requires removal of existing inertial reference units (IRU) and installation of modified IRU's. This amendment is prompted by a report of the failure of the left and center IRU's on a single flight. The actions specified by this AD are intended to prevent loss of multiple IRU's in flight, which could result in the loss of navigation data during flight. This could compromise the ability of the flight crew to maintain the safe flight and landing of the airplane.
To prevent loss of multiple IRU's in flight, which could result in the loss of navigation data, and compromise the ability of the flight crew to maintain the safe flight and landing of the airplane, accomplish the following:
(a) Within 18 months after the effective date of this AD, remove the left, center, and right IRU's, and install modified IRU's, in accordance with Boeing Alert Service Bulletin 747-34A2638, Revision 1, dated April 8, 1999.
Note 2: Removal of existing left, center, and right IRU's and replacement with modified IRU's in accordance with Boeing Alert Service Bulletin 747-34A2638, dated January 29, 1999, is considered acceptable for compliance with paragraph (a) of this AD.
(b) As of the effective date of this AD, no person shall install an IRU having Boeing part number S242T101-110, S242T101-111, or S242T101-112, on any airplane.
