Emergency AD Issued On B737 Max

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The FAA has issued an Emergency Airworthiness Directive (PDF) that directs the owners of all Boeing 737 Max aircraft to amend their operating manuals, to avoid a control problem like the one that apparently caused the fatal crash of a Max 8 last week. “Possible erroneous angle-of-attack inputs on Boeing 737 Max aircraft … can potentially make the horizontal stabilizers repeatedly pitch the nose of the airplane downward, making the aircraft difficult to control," the FAA says in an emergency AD dated Nov. 7. The airplanes are not grounded, and the owners have three days to comply with the AD, which requires a revision to the airplane flight manual.

“This emergency AD was prompted by analysis performed by the manufacturer showing that if an erroneously high single angle of attack (AOA) sensor input is received by the flight control system, there is a potential for repeated nose-down trim commands of the horizontal stabilizer,” the AD reads. “This condition, if not addressed, could cause the flight crew to have difficulty controlling the airplane, and lead to excessive nose-down attitude, significant altitude loss, and possible impact with terrain.” The AD requires revising certificate limitations and operating procedures to provide the flight crew with runaway horizontal stabilizer trim procedures to follow under certain conditions.