Semantron 23 Summer 2023

The Boeing 737 Max crisis

10. Trimmable Horizontal Stabilizer (THS): Horizontal Stabilizer controls the pitch of an aircraft, i.e. nose up or nose down. It is needed to be trimmed to a correct angle to maintain pitch in-flight, or for take-off and landing. This can be controlled by physical pilot input (electric trim or manual wheel trim), or automatically with a fly-by-wire system.

Figure 26: THS on an Embraer ERJ-190 jet. The markings represent the angle that the stabilizers are trimmed to.

11. Flight Director: Flight Director, or F/D, is an instrument on board an aircraft, which is shows on the altitude indicator, showing the pilots the pitch (and altitude) the aircraft should be aiming for, in order to follow the pre-set trajectory. The F/D is usually shows as a ‘ cross ’ on the monitors.

Figure 27: This is the PFD of a B737 aircraft. The pink cross shows is the F/D.

12. Emergency Airworthiness Directives: Issued by aviation authorities when an unsafe condition has been identified which requires immediate actions by the aircraft owner or operator. An Emergency AD outlines what operators and manufacturers have to do in order to preserve the aircrafts’ airworthiness.

13. Alert Service Bulletin: Issued by manufacturers, when a safety hazard has been identified. It contains description of the potential hazard, then provides technical information on how to resolve the hazards.

Appendix 3: figures bibliography

Fig 1: Ostrower, J. (November 7, 2018), ‘Boeing issues 737 Max fleet bulletin on AoA warning after Lion Air crash’. The Air Current . warning-after-lion-air-crash/. Consulted April 7, 2022. Fig 2: Federal Aviation Administration, Airworthiness Directives AD 2018-23-51 . Consulted April 7, 2022. Fig 3: The Boeing 737 Technical Site, Sales . Consulted February 19, 2022. Fig 4: Leeham News and Analysis (November 17, 2014), ‘A320 v B737: the sales winner is…’. Leeham News and Analysis . Consulted February 23, 2022. Fig 5: Infinite Flight Forum, A Guide to Fly-By-Wire . wire/110427. Consulted March 25, 2022. Fig 6: pdxlight, Airbus A320neo + Boeing 737MAX – orders and commitments . Consulted March 25, 2022. Fig 7: Engineer Waqar, What is a Turbofan Engine | How does a Turbofan work? Consulted March 25, 2022. Fig 8: Fehrm, B. (November 20, 2020), ‘Bjorn’s Corner: 737 MAX ungrounding, the technical background’. Leeham News and Analysis . technical-background/. Consulted March 25, 2022. Fig 9: SKYbrary, Angle of Attack (AOA) . Consulted March 25, 2022. Fig 10: Pilotfriend, stalls . Consulted March 25, 2022. Fig 11: Gates, D. (August 20, 2019), ‘FAA cautions airlines on maintenance of sensors that were key to 737 MAX crashes’. Seattle Times. maintenance-of-sensors-that-were-key-to-737-max-crashes/. Consulted March 2, 2022.


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