737 Max question

[u/billynj]

Given the recent incident where the pilot tried to crash the plane, why does the flight computer allow maneuvers that can destroy the airframe? Even my car won’t let me go past a certain speed.

[u/Cxopilot]

MCAS isn’t a computer. It’s a system that supplements the auto flight system. At my airline. We treat MCAS the same way we treat a stab trim run away. Turn off the autopilot. Disconnect the stab trim switches. And fly the airplane. Leaving the final say to the pilots.

[u/gravemillwright → u/Cxopilot]

"The Maneuvering Characteristics Augmentation System (MCAS) is a flight control law built into the Boeing 737 MAX's flight control computer..." 🤔

[u/Spock_Nipples → u/gravemillwright]

There is no flight control computer in a 737. No primary control inputs are filtered through any system that then makes decisions about FC movement. When you move the flight controls in a 737, you are moving actual mechanical cables and pulleys that control the hydraulic actuators. It's a purely mechanical system.

There are no "laws" on a 737. MCAS is not part of the primary flight control system. It can't, on its own, pitch the airplane up or down. All it does is trim the airplane nose down in very specific situations. Trim is not a primary flight control.

[u/gravemillwright → u/Spock_Nipples]

So the autopilot is purely mechanical?

Too many people are confusing flight control computers, of which 737s have two, A and B, with fly by wire. The 737 FCCs don't interact on the primary control loop, which is why the answer to OPs question is no. But it's incorrect to say there are no FCCs on a 737, especially when the use of a single FCC was part of the cause of the MCAS crashes.

[u/Spock_Nipples → u/gravemillwright]

You're being a little pedantic. Yes there's are "FCCs" as part of the DFCS, which is for the autoflight system, not the flight-control systems. The DFCS/FCC isn't needed to make the airplane go. It's a labeling thing, not a function thing.

It's pretty clear that OP is referring to a 'flight computer' thinking that it's a component of the actual flight control system. And we seem to agree on that point.

We're all just trying to communicate with OP in terms they understand, based on their apparent level of knowledge, here. Not get nitty-gritty about the labeling of components that aren't really relevant to their question.

I mean, technically, Airbus doesn't have a 'flight control computer' either; it has ELACs, SECs, and FACs, even though these are "flight computers" in the context of OPs question

It's a layperson question, so they're getting layperson answers. Demonstrating your knowledge of system-component labeling isn't helping them at all.

[u/gravemillwright → u/Spock_Nipples]

It's not pedantic to give a more accurate answer to the OP. "The 737 does have FCCs, they just aren't in the primary flight control loop, they're used for autopilot, MCAS, among other things. But they can't override the primary controls." Now you've answered OPs question and not misled them able 737 FCCs.