Airworthiness Directive · Amendment 39-15609 · Boeing Model 747-400 and 747-400D Series Airplanes
Boeing Model 747-400 and 747-400D Series Airplanes
This AD applies to Boeing Model 747-400 and 747-400D series airplanes, certificated in any category; as identified in Boeing Special Attention Service Bulletin 747-24-2257, Revision 1, dated August 2, 2007.
We are adopting a new airworthiness directive (AD) for certain Boeing Model 747-400 and 747-400D series airplanes. This AD requires a general visual inspection of the power feeder wire bundle of the auxiliary power unit (APU) where it crosses the hydraulic system 4 return tube to determine if parts are installed to provide separation between the wire bundle and hydraulic tube. This AD also requires related investigative and corrective actions if necessary. This AD results from a report that the power feeder wire bundle of the APU was found touching the hydraulic system return tube during inspection of an airplane. We are issuing this AD to prevent insufficient clearance between the wire bundle and hydraulic tube that could lead to chafing of the wire bundle, which could cause arcing and a consequent hydraulic fluid fire in an area outside of the smoke detection and fire extinguishing zone; this condition could result in an uncontrolled fire on the airplane.
You are responsible for having the actions required by this AD performed within the compliance times specified, unless the actions have already been done.
Within 24 months after the effective date of this AD, do a general visual inspection of the power feeder wire bundle of the APU where it crosses the hydraulic system 4 return tube to determine if parts are installed to provide separation between the wire bundle and hydraulic tube, and do all the related investigative and corrective actions as applicable, by accomplishing all of the actions specified in the Accomplishment Instructions of Boeing Special Attention Service Bulletin 747-24-2257, Revision 1, dated August 2, 2007. The related investigative and corrective actions must be accomplished before further flight after the inspection.
Actions done before the effective date of this AD in accordance with Boeing Special Attention Service Bulletin 747-24-2257, dated May 18, 2006, are acceptable for compliance with the corresponding requirements of paragraph (f) of this AD.
