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

The FAA is adopting a new airworthiness directive (AD) for certain Boeing Model 747-400, 747-400D, 747-400F, 757-200, 767-200, 767-300, and 767-300F series airplanes. This AD requires inspecting to determine the date code of the time delay relay for the cargo fire suppression system, and replacing the relay if necessary. This AD results from a report indicating that failure of a time delay relay on an ELMS (electrical load management system) panel led to testing of other time delay relays at Boeing and at the supplier. Similar relays are used in the cargo fire suppression system. The time delay relay controls when the secondary fire bottles discharge. We are issuing this AD to ensure there is sufficient fire suppressant to control a cargo fire if the airplane is more than the relay delay time from a suitable airport, which could result in an uncontrollable fire in the cargo compartment.