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by phugoid 2349 days ago
> Do simulators have the same hardware as real planes, or do they have a software model of the airplane?

If you're looking at the highest fidelity level D simulators, the instruments and controls in the cockpit are either the same parts as the aircraft, or functionally identical (but cheaper).

> If you simulated a broken AoA sensor, would the simulated plane behave similar to the real plane? Would the MCAS system have the same bugs in the simulator as in the one in the real aircraft?

One of the big costs in building a simulator is buying the data package from the aircraft manufacturer, with the aero model and details of system internals, things like electrical and hydraulic schematics. Sim makers build a software model of these internals at a pretty low level. For the most part, if you introduce a fault in some part of the system it will behave the right way as an emerging property, not because you're forcing the system to have the right outputs.

Some software components from the aircraft get installed on the simulator with the same hardware platform from the aircraft, others get run as executables on the simulator's computers, and others get re-implemented from scratch (lots of FORTRAN and C).

That kind of detail comes into play when the instructors introduce multiple failures at the same time - pilots have to take corrective actions to make the faults go away or manage them - if you don't model the systems at a pretty low level you'll never high fidelity.

> Can you try new scenarios in a simulator, or can you just try scenarios that the simulator was designed to run?

There is a list of malfunctions available to the instructor, who runs the session from the back of the "cockpit" on touch panels. For the most part, these malfunctions cover failures that are anticipated by the aircraft manufacturers, and the corrective actions / system behavior are well understood. Each fault is tested to make sure it works properly. You don't go and fail some random component in the system.

When an important failure happens in the real aircraft, it might get added as a training scenario to simulators already in operation.

1 comments

> You don't go and fail some random component in the system.

I always wondered if they did that, something akin to fuzzing tests in SW. Wouldn't it be useful to detect unexpected situations that'd be catastrophic? Or the benefits from it wouldn't outweigh the cost/time loss?

Even with a pretty good model, if you introduce new failures that were not anticipated/tested, there's a risk that the system will not behave as per the aircraft. Now you're giving "negative training" to your pilots, maybe worse than no training at all.

Also, imagine you're an airline with thousands of pilots and dozens of instructors: you're running an airline and a school at the same time. You need to build a curriculum of training and testing that will standardize your pilots. There's room for thinking outside the box but not too much.

Good point, thanks for your insights!
Keep in mind that this is a simulator for training the crew. This is not a hardware testbed. These are separate beasts entirely. There are all kinds of setups from component tests up to system integration testing. My understanding is that the impact of component failures is tested on these hardware integration testbeds.
I always wondered if they did that, something akin to fuzzing tests in SW.

Well Boeing certainly doesn't fuzz their software as evidenced by the major bugs in the 737 NG and 747-400's flight displays. Both had bugs that would black out all instruments under specific conditions. That got fixed fairly quickly on the 747, but apparently Boeing didn't learn their lesson with the NG.

The bug didn't black out all instruments, it blacked out the multi-function displays. Certainly less than ideal, but that's precisely why backup instruments exists.
The bug didn't black out all instruments, it blacked out the multi-function displays. Certainly less than ideal, but that's precisely why backup instruments exists.

The bug blacked out all six display units. What other instruments are you thinking of?

All critical instruments have analog backups. Altitude, speed, artificial horizon, etc.