Summary
The FAA proposes to adopt a new airworthiness directive (AD) for certain smoke detectors installed on various transport category airplanes. This proposed AD would require replacing the affected smoke detectors with modified smoke detectors. This proposed AD is prompted by a report indicating that the affected smoke detectors can "lock up" during electrical power transfer from the auxiliary power unit to the engines. We are proposing this AD to identify and provide corrective action for a potentially inoperative smoke detector and to ensure that the flightcrew is alerted in the event of a fire.