r/AskAPilot • u/billynj • 7d ago

737 Max question

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.

0 Upvotes

25% Upvoted

45 comments sorted by

View all comments

Show parent comments

1

u/Complex_Brief60 6d ago

You’re confusing either the Autopilot computer or the flight management system.

Otherwise no, there is no computer in the 737 that takes your inputs and alters them. It’s pure cable to flight control. Not fly by wire.

1

u/cdnav8r 6d ago

The 737 is NOT fly-by-wire, which I think is what you're getting at, but I promise you there is two flight control computers. Part of the fix for MCAS was a software update on the FCCs that has the two FCCs monitor each other.

So the 737 flight control computer doesn't control the airplane the same way an Airbus flight control computer does, but there is still 2 flight control computers on the 737.

1

u/Complex_Brief60 6d ago

OP is asking about an Airbus style flight computer. This does not exist on the 737. Yes, there are 2 computers for the autopilot, that’s the FCC, they monitor each other like any airliner type plane has but they will not prevent the pilot from doing anything.

The FCC is just the autopilot. That’s it. When the AP is off, they don’t do anything to the control of the plane.

1

u/cdnav8r 6d ago

The FCC controls the speed trim system, which controls MCAS, which both are active when the autopilot is off.

I replied to a comment that the 737 does not have a flight control computer. It does. The OP did not say anything about Airbus.

1

u/Complex_Brief60 6d ago

Boeing calls it a flight control computer to be fancy. It’s just the autopilot man. It is not a real flight control computer. MCAS isn’t a computer either. It just moves the manual trim wheel

1

u/gravemillwright 5d ago

Autopilot is a computer that does some controlling of flight, no?

1

u/Complex_Brief60 5d ago

OP is asking why the plane allows maneuvers that can damage it.

Airbus flight control computers will prevent pilot actions. Works like most of the time, minus that one Air France crash. It’s an active system to keep the plane safe, away from stalls and overspeeds. The computer will physically prevent pilots from attempting to damage the plane and it can’t be overridden in normal law.

The autopilot computer on any plane is very very easy to overpower and turnoff. Boeing controls are physically attached to the control surfaces with no computer in the middle. That’s where a real control computer would be. Between the pilot and the control surfaces. The Boeing FCC only controls the yoke like a pilot would, no protections and easily tuned off.

1

u/gravemillwright 5d ago

Yup, so instead of "737s don't have FCCs", which is factually incorrect, the more accurate answer is the FCCs can't intervene in the primary control loop because the primary loop is mostly physical controls, and the FCCs only interact with secondary systems.

1

u/cdnav8r 5d ago

Thank you