AD FAA-2020-0686

The FAA is superseding Airworthiness Directive (AD) 2018-23- 51, which applied to all The Boeing Company Model 737-8 and 737-9 (737 MAX) airplanes. AD 2018-23-51 required revising certificate limitations and operating procedures of the Airplane Flight Manual (AFM) to provide the flightcrew with runaway horizontal stabilizer trim procedures to follow under certain conditions. This AD requires installing new flight control computer (FCC) software, revising the existing AFM to incorporate new and revised flightcrew procedures, installing new MAX display system (MDS) software, changing the horizontal stabilizer trim wire routing installations, completing an angle of attack (AOA) sensor system test, and performing an operational readiness flight. This AD also applies to a narrower set of airplanes than the superseded AD, and only allows operation (dispatch) of an airplane with certain inoperative systems if specific, more restrictive, provisions are incorporated into the operator's existing FAA-approved minimum equipment list (MEL). This AD was prompted by the potential for a single erroneously high AOA sensor input received by the flight control system to result in repeated airplane nose-down trim of the horizontal stabilizer. The FAA is issuing this AD to address the unsafe condition on these products.