Summary
The FAA is revising an earlier proposed airworthiness directive (AD) for certain Boeing Model 757 airplanes. The original NPRM would have required inspections of certain wire bundles in the left and right engine-to-wing aft fairings for discrepancies, and related investigative and corrective actions if necessary. The original NPRM was prompted by a report indicating that a circuit breaker for the fuel shutoff valve tripped due to a wire that chafed against the structure in the flammable leakage zone of the aft fairing, causing a short circuit. This action revises the original NPRM by adding a new requirement for installing back-to-back p-clamps between the wire and hydraulic supply tube at the aft end of the right-hand strut only; and associated re-routing of the wire bundles, if necessary; and adding airplanes to the applicability. This action also clarifies the applicability specified in the original NPRM. We are proposing this supplemental NPRM to prevent chafing between the wire bundle and the structure of the aft fairing, which could result in electrical arcing and subsequent ignition of flammable vapors and possible uncontrollable fire.