Semantron 23 Summer 2023

The Boeing 737 Max crisis

have an AoA warning system onboard, including Lion Air & Ethiopian Airlines which crashed in 2018 and 2019.

Additionally, MCAS was designed to accept two separate inputs – the AoA sensor and the g-force input. 50 Collins Aerospace later decided to take only one AoA Sensor reading, and would not take any g-force reading, meaning that when one of them is faulty, MCAS has no idea which is faulty and which is not, and it may pick the faulty one, thus reading incorrect flight data, and carrying out the wrong instructions. Prior to the update of the MCAS, it automatically conducted AND for 9.26 seconds at an angle of 2.5°, and pause for 5

seconds before checking the data again. 51 If the data is still unreliable, MCAS will repeat the process again. The only way to disable MCAS, is to switch off the STAB TRIM CUTOUT switches.

Figure 12: MCAS

According to the Quick Reference Handbook (QRH) of the Boeing 737NG aircraft, when the aircraft is experiencing RUNAWAY STABILIZER , or the Autopilot (A/P) does not set the trim correctly, it is listed that the pilots should hold firmly of the control column, disengage A/P, cut out STAB TRIM CUTOUT switches (if electric trim is not working), then trim manually using the mechanical way. 52 It is also worth noting that the procedure of RUNAWAY STABILIZER , STABILIZER OUT OF TRIM and STABILIZER TRIM INOPERATIVE are memory items for

Figure 13: STAB TRIM CUTOUT switches on the control column

pilots, meaning that every pilot should be able to memorize the recovery procedures without checking the QRH due to its urgency. Boeing’s plan was to attract airlines to purchase the MAX aircraft as it required minimal training to switch the type rating from B737NG to B737 MAX. According to the New York Times , ‘ many pilots with 737 experience learned about the plane on an iPad ’ . 53 There wasn’t even a simulator training session for pilots to switch between the older generation to the newer generation. Boeing also submitted a request to the FAA, requesting to remove MCAS contents from the flight manual, 54 making it look even more like the previous generation of aircraft, eventually, leaving pilots behind, without them knowing what the system actually is, or how to disable it. ‘ In addition to a two- hour iPad training cour se from Boeing, he and colleagues used their experience […] to create a 13 -page

50 Coughlin 2020, Crashing the 737 MAX, Revision 1 : 13.129. 51 Brady 2021, The Boeing 737 Technical Guide, 83 rd ed : 71. 52 2009, 737 Quick Reference Handbook : 9.1, 9.14, 9.15. 53 Gelles, et al. 2019, After 2 Crashes of New Boeing Jet, Pilot Training Now a Focus . 54 Laris 2019, Changes to flawed Boeing 737 Max were kept from pilots, DeFazio says .


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