Airworthiness Directives; Boeing Model 767-300 Series Airplanes

The FAA is adopting a new airworthiness directive (AD) for certain Boeing Model 767-300 series airplanes. This AD requires repetitive functional tests and repetitive replacements of the auxiliary power unit (APU) and engine fire shutoff switches. This proposal also provides an optional terminating action for the repetitive functional tests and replacements. This AD is prompted by a report of the failure of the engine fire shutoff switch in the engine fire control module. We are issuing this AD to prevent mineral build-up on the APU and engine fire shutoff switches, which could lead to the switches failing to discharge fire suppressant to the affected fire zone and result in an uncontrolled engine or APU fire and consequent loss of the airplane.