Operators of about 500 Boeing 737 aircraft would have to replace or upgrade autothrottle computers to comply with a proposed airworthiness directive published by the FAA on Monday. The AD would mandate actions that Boeing already has recommended to operators via service bulletins. The AD was “prompted by reports in which a single, undetected, erroneous radio altimeter output caused the autothrottle to enter landing flare retard mode prematurely on approach,” the FAA said. “We are issuing this AD to prevent a single, undetected, erroneous radio altimeter output from causing premature autothrottle landing flare retard and subsequent loss of automatic speed control, which could result in loss of control of the airplane.”
According to The Wall Street Journal, the proposed AD stems from the 2009 crash of a Turkish Airlines 737, which crashed short of an Amsterdam runway after a faulty altimeter caused the automated throttles to prematurely roll back thrust. Nine people were killed. Operators will have three years to upgrade the autothrottle computer after the effective date of the AD. The work only takes about an hour, and there is no cost for parts for the operators, according to the FAA.
