Airworthiness Directives; Boeing Model 747-400, 757-200, 767-200, and 767-300 Series Airplanes

This amendment adopts a new airworthiness directive (AD) that is applicable to certain Boeing Model 747-400, 757-200, 767-200, and 767-300 series airplanes. This action requires repetitive checks to detect certain failures in the warning electronic unit (WEU) or modular avionic warning electronic assembly (MAWEA); repetitive tests to detect any failure of tactile, visual, or aural alert generated by the WEU or MAWEA; and corrective action, if necessary. This AD also provides for an optional terminating action for the repetitive checks and tests. This amendment is prompted by a report of a MAWEA power supply failure due to inadequate over-voltage protection. The actions specified in this AD are intended to detect and correct such a failure, which could result in loss of visual, aural, and tactile alerts to the flightcrew. Absence of such alerts could result in the flightcrew being unaware that an immediate or appropriate action should be taken in the event of an unsafe condition.