Semantron 23 Summer 2023

The Boeing 737 Max crisis

aircraft gave no response, 72 and kept descending. Shortly after that, the pilots reactivated the electric trim by turning off the STAB TRIM CUT-OUT . This meant MCAS could now be reactivated, and it was. At 05:43:25 UTC, MCAS gave its 4 th AND command, pushing the plane down, and impacting the ground at 05:43:43 UTC. 73

If the AND and ANU function has been disabled, why didn’t the manual trim work? According to the DFDR, the engine maintained at the Take Off thrust, at 94% N1 thrust throughout the whole flight. 74 This caused the aircraft to continue to accelerate, eventually overspeeding at 05:41:32 UTC, reaching an airspeed of 350 knots (ground speed of 420 knots, or 593 km/h, or 369 mph). 75 However, both the manual trim and electric thumb-switch trim do not actually work when the aircraft is at Overspeed, due to high aerodynamic loads. 76 ‘ Trim certification requirements from the

Figure 15: Recorded Flight Data for ET302, (blue: altitude, red: ground speed, green: vertical speed)

European Union Aviation Safety Agency state that the aircraft must maintain longitudinal trim in level flight up to the V mo (Maximum Operating Limit Speed) limit speed, with the landing-gear and flaps retracted. ’ 77 This was actually intended to increase safety, preventing pilots from over-trimming, forcing the plane to dive down when overspeeding, which could cause loss of control.

After the second crash, the FAA had no plans to ground the B737 MAX aircraft, stating ‘ we have not been provided data to draw any conclusions or take any actions ’ . 78 One day after the crash of ET302, on 11 th March 2019, the China Civil Aviation Administration suspended all commercial operations of B737 MAX aircraft. 79 China and Indonesia became the first two countries to ground the aircraft, followed by Singapore, India, Turkey, Australia, the EU, South Korea, Vietnam, Malaysia and many more. This left over 700 MAX aircraft grounded in nearly 100 locations, including those newly built by Boeing but not yet delivered. 80 When the planes had to be flown to storage facilities all over the globe, it was reported that pilots were reluctant in flying the aircraft – even the pilots

did not trust the aircraft. ‘ When a pilot doesn’t want to fly a brand -new Boeing, that’s an issue,’ added one of the pilots

Figure 16: Grounded B737 MAX aircraft in Parking Lot 0974, in Moses Lake, Washington, USA. Image taken on 18/02/20.

72 Coughlin 2020, Crashing the 737 MAX, Revision 1 : 38. 73 Ibid. 74 Aircraft Accident Investigation Bureau 2019, Aircraft Accident Investigation Preliminary Report – ET-AVJ: 9, 27. 75 Ibid. 76 Davydov 2022, Email Questionnaire with Captain Denys Davydov by Matthew Wu . 77 Kaminski-Morrow, Ethiopian crew struggled with manual trim at overspeed . 78 Pasztor et al. 2019, The FAA Has No Current Plans to Ground Boeing’s 737 MAX After Deadly Crash . 79 Lahiri 2019, China is the first country to ground the Boeing 737 Max after its two crashes . 80 Petchenik 2019, Where the grounded 737 MAX are stored .


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