The US FAA is set to release a final airworthiness directive tomorrow requiring operators of more than 500 legacy Boeing 737 models (-100 though -500) to replace certain wire bundles in the outboard landing light and fuel shutoff valve wire harnesses within five years at a total cost of approximately $13 million fleet-wide.
The required replacements, outlined in a 2007 Boeing Service Bulletin, occur after reports of uncommanded engine shutdowns due to "hot shorts" caused by burned and damaged wires in bundles that run to the aircraft's landing lights and engine fuel shutoff valves.
As a preliminary safety measure, FAA is requiring the same operators to deactivate or modify the wiring to the outboard landing lights within six months of the rule's mid-August effective date to prevent a short circuit and possible engine shut down.
FAA warns operators that aircraft, with the outboard landing lights disabled, cannot be released for night flights if either of the inboard landing lights has failed.
Other anomalies addressed in the AD include inspections for broken, damaged or missing electrical leads, grommets and wires in four electrical junction boxes of the main wheel well, and replacement of certain electrical connectors in US-registered aircraft.