Editing Thrust (section)

===Thrust axis===

The thrust axis for an airplane is the [[line of action]] of the total thrust at any instant. It depends on the location, number, and characteristics of the jet engines or propellers. It usually differs from the drag axis. If so, the distance between the thrust axis and the drag axis will cause a [[moment (physics)|moment]] that must be resisted by a change in the aerodynamic force on the horizontal stabiliser.<ref>Kermode, A.C. (1972) ''Mechanics of Flight'', Chapter 5, 8th edition. Pitman Publishing. {{ISBN|0273316230}}</ref> Notably, the [[Boeing 737 MAX]], with larger, lower-slung engines than previous 737 models, had a greater distance between the thrust axis and the drag axis, causing the nose to rise up in some flight regimes, necessitating a pitch-control system, [[Maneuvering Characteristics Augmentation System|MCAS]]. Early versions of MCAS malfunctioned in flight with catastrophic consequences, leading to the [[Boeing 737 MAX groundings|deaths of over 300 people]] in 2018 and 2019.<ref>{{Cite web|url=https://www.aljazeera.com/news/2019/03/control-system-scrutiny-ethiopian-airlines-crash-190311094532350.html|title=Control system under scrutiny after Ethiopian Airlines crash|website=Al Jazeera|access-date=7 April 2019|archive-url=https://web.archive.org/web/20190428062403/https://www.aljazeera.com/news/2019/03/control-system-scrutiny-ethiopian-airlines-crash-190311094532350.html|archive-date=28 April 2019|url-status=live}}</ref><ref>{{Cite web|url=https://theaircurrent.com/aviation-safety/what-is-the-boeing-737-max-maneuvering-characteristics-augmentation-system-mcas-jt610/|title=What is the Boeing 737 Max Maneuvering Characteristics Augmentation System?|date=14 November 2018|website=The Air Current|language=en-US|access-date=7 April 2019|archive-url=https://web.archive.org/web/20190407184426/https://theaircurrent.com/aviation-safety/what-is-the-boeing-737-max-maneuvering-characteristics-augmentation-system-mcas-jt610/|archive-date=7 April 2019|url-status=live}}</ref>