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Comment by weaksauce | Hacker News Reader

I’m curious why they would need that system in the first place. Pilots know to trim for level flight so the computer doing it automatically seems unneeded regardless of new engine placement.

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The engines are more powerful and further ahead of the wing on the MAX. This means that the plane may pitch up significantly (and potentially stall) if you apply a bunch of thrust. MCAS was designed to prevent this.

There was, IIRC, a similar incident in an 737 Classic (go around in England that achieved a dramatic nose up pitch IIRC — not the Tailwind incident) but I can't seem to find the entry on avhearld.

You're probably referring to this one - Thomson 737-300 at Bournemouth in 2007. Scary reading the full report: 44 degrees nose-up and 82 knots indicated air speed!

https://www.gov.uk/aaib-reports/aar-3-2009-boeing-737-3q8-g-...

Yep, that's the one. If memory serves, most or all planes with the engines under the wing will pitch up when you apply thrust. Most planes will have an effective enough elevator to counteract this... but it seems like the 737 does not.

The new system (MCAS) was not intended to take action in normal flight. It was intended the trim in certain scenarios (roughly high AoA + steep turn + high g + near stall), but on lion air 610 the AoA sensor was malfunctioning, which caused MCAS to activate when it shouldn't have.

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