In a flight in the same plane the day before, to Jakarta, the pilot experienced many of the same symptoms as the pilots on flight JT610: the stick shaker activated during rotation, an indicated airspeed warning alert appeared, and the aircraft began automatically pushing the aircraft nose down. pilots encountered problems involving the AoA as well as the pitot tube used to measure airspeed. (Original source is the Preliminary Report from that accident). The previous LionAir crews on the accident aircraft ended up flying to their destination manually. It is unclear how many of the crews knew that it was MCAS that was malfunctioniing, versus any other trim or pitch anomaly. The manual pitch trim procedure appears to be what a few crews did prior to the LionAir crash in October 2018. This means that the pilots must move/rotate the trim wheels in order to apply pitch trim during flight, though the Max trim wheels being of a smaller diameter raises a training and effectiveness problem 1 that deserves its own question and answer. This disables the horizontal stabilizer's trim completely, and reverts to manual trim ( there are two guarded stabilizer trim switches in the aisle stand, see Windshear's answer). It is intended to work only if the flaps are up. The easiest fix was to automatically apply a little nose down trim at high angles of attack.Ī few things that should disable it (with caveats) It is only there because the larger engine nacelles of the B737 MAX cause an aerodynamic pitch up moment at high angles of attack that did not meet FAA longitudinal stability and stick force certification standards. MCAS does not counter the additional thrust of the more powerful engines. Just about everything you have read in the media is wrong.The observation was a follow up to an observation that the MCAS isn't an anti stall feature like a stick shaker, but rather. Its activation requires a number of preconditions, but we'll get to that in a moment.Ī concise description of the system is found here. It is a fly-by-wire feature designed to account for a particular flight regime that would not (or was not expected to be) encountered very often in normal operations, and is intended to account for some of the aerodynamic effects of the LEAP-1B (CFM International) engine installation for this model.
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