[JoshTriplett]

On trains, "stop" is generally a safe action. On planes in the air, "stop" is a deadly action.

As described, that sounds like a mechanism that could potentially go very wrong on a plane. By way of example, consider if the plane was in flight and a door opened: the pilots need full control of the plane in order to land it.

There should absolutely be mechanisms to detect and avoid this situation, but hard interlocks like you're describing could cause catastrophic failures in flight.

[littlestymaar]

> On trains, "stop" is generally a safe action. On planes in the air, "stop" is a deadly action.

Having worked in this industry (edit: train industry) I'm fully aware of that.

> By way of example, consider if the plane was in flight and a door opened the pilots need full control of the plane in order to land it.

Not necessarily. Or at least it depends how you define “full control”: of course everything related to flight is mandatory. But, for instance, the ability to unlock the parking brakes of the landing gear likely isn't something you need while piloting mid-air and this is enough to implement the safety mechanism I talked about.

Also, you could have a bypass for the safety lock in case something goes wrong. For instance in PWR nuclear reactors, you don't want to accidentally overflow the steam generator, so there's one pump, designed to feed it when the reactor is stopped, that is disabled when the reactor is running. But in case of accident you may actually need this pump, so there's a key (literally a physical key) that you can use to disable the protection and make the pump usable in that mode too.

[throw_a_grenade]

In flight maybe not, but after flight there comes landing, and landing on wheels that have parking brake engaged (because of that interlock) may or may not be safe. Yeah, you can add logic to prevent that, you can add more manual overrides, but eventually there's a point when new feature (even one added "for safety") will cause more problems that it will solve.

[littlestymaar]

That's true that there's a balance between the safety benefit you get from the feature and the overhead it ads for the operators (the key example in nuclear reactor I was talking about has actually caused a issue once leading to the enforcement not an additional procedure around it).

What I meant in my response is that the answer cannot simply be “interlocking in a plane would be too dangerous”, so my original question still stands: why is it the case in airplanes when it looks so fucked up from a train perspective.

[JoshTriplett]

> Also, you could have a bypass for the safety lock in case something goes wrong. [...] there's a key (literally a physical key) that you can use to disable the protection

I'm entirely in favor of having a safety mechanism with explicit warnings and a bypass mechanism, with that bypass mechanism being something that should never happen in normal operation.

I was solely arguing against the kind of interlock that a train has where "current can't flow" if the doors are open, since the plane should absolutely be able to operate with the doors open in order to safely land.

[littlestymaar]

I understand what you mean. Just to clarify, when I said current couldn't flow it's obviously some dedicated very low voltage current that is merely supposed to act a sensing mechanism, it's the not actual current powering the train that is being cut hard by the doors.