[BenoitP]

"- A component of the main electric trim system became inoperative. Our pilots ran the appropriate checklist, which included manually trimming the aircraft. They returned to MIA and landed uneventfully. The issue was not related to MCAS."

I don't get it. It is common for other airliners to rely systematically on trimming? Do other airliners have similar 'correcting' systems as MCAS?

[dghlsakjg]

Almost every airplane except the absolute most basic have trim controls for flight surfaces, especially the elevator. Even little two seat Cessnas get trim controls.

Trim is changed for each phase of flight. Electric trim is just a motor spinning the manual trim control.

Most airliners will be doing constant trim adjustment.

If you want a real change of pace check out Airbus’ control system. It does a lot more intervention than anything Boeing does. Depending on the state of the aircraft the control stick will respond to input in entirely different ways (3 ‘laws’ that contain no less than 5 submodes). Sometimes it will act as you would expect a stick to act, other times it will intentionally limit what the pilot is asking of the plane, sometimes it will average what the two pilots are asking. Confusion about how the system works has caused at least two crashes I can think of (AF447, QZ8501). It’s killed more people than the Max, but it was written off as pilot error since it was operating as designed in both cases. It just happens to be a design that will change the way the plane is controlled when things go wrong. A few of the modes do in fact include automatic trim adjustments.

[bonzini]

AF447 was definitely pilot error, not realizing that the aircraft was stalling.

[slacktide]

Predicated on their assumption that the flight control laws would prevent a nose-up control input from stalling the aircraft, and not realizing that the aircraft was in alternate law. Some of the last words on the CVR from the pilot flying were “But I’ve been at maxi nose-up for a while” while the computer was shouting STALL STALL STALL in the background.

[VBprogrammer]

You ever have the experience when you listen to someone speak with a strong accent, you don't quite catch the beginning of a word and the whole of what they say sounds like a foreign language?

I imagine that is how those poor pilots felt as their instruments screamed conflicting information at them as they tore through the skies above the mid-atlantic.

[mrguyorama]

A huge problem with that incident is that as the plane got deeper into the stall, the computer decided it couldn't get an accurate idea of what was going on and STOPPED giving the stall warning. This lead to the crummy situation where pulling back on the stick made the warnings go away, despite being the exact opposite control input required.

This situation is 100% opposite of basic stall recovery, but I don't know how much that still works when you are panicking and no longer feel like you can trust your instruments or your plane

[VBprogrammer]

The phrase "the computer decided" gives way more agency to the computer than it deserves in this instance. In reality it was a simple airspeed threshold below which no one imagined the aircraft actually flying.

It was a really tragic accident with many lessons for anyone involved in the design of critical systems.

[airhead969]

Yeap. The electric trim systems tend to be automatic with speed and altitude to approximate what the pilot wants via trim up/down controls. Without trim, planes would be pitching and diving all over the place, or at least require yoke/sidestick back-pressure to hold steady. Some planes can be trimmed through enormous deflections of the horizontal stabilizer. If configured incorrectly and under the wrong conditions, incorrect trim can lead to dangerous flight characteristics like pitching up or down beyond what the elevators can handle at full deflection. A broken jackscrew (part that moves the horizontal stabilizer for the trim commands) can cause this type of dangerous configuration or even worse.

[danaliv]

Even gliders have trim. It's not technically considered a primary flight control because you can survive without it, but at the very least it's annoying not to have it.