If a pilot ejects, what is the autopilot programmed to do?

This is why my favorite coffee table book is the “XKCD What If”. He only spends a few seconds on “why it probably wouldn’t happen”, then fully digs into what would happen if it did.

But isn't the answer kind of the same? Undefined behavior will result.

It's literally not something that gets programmed though. It's like asking "if Microsoft Word stops responding and I press the close button, is it programmed to auto-save my file?" It could not possibly get to that point where it could execute such instructions, so it makes no sense to program that behavior in.

My experience with aircraft autopilots is limited. I've used them in small planes (altitude hold, heading hold types). I have read about them on commercial and military jets, in order to simulate them for a flight simulator.

With that caveat, every autopilot system I've studied turns itself off if the plane is outside its flight regime. So for example, if you pull a plane straight up and do a tail stall and try to turn on the autopilot, the autopilot would refuse to engage as the plane isn't in a "flyable" regime.

What is more, the autopilots I've seen were explicitly programmed to be pilot activated, so even if the plane went from one regime where the autopilot kicked itself off automatically, back to one where the plane could be flown by the autopilot, the autopilot would not automatically re-engage.

If the pilot ejects because they cannot control the plane, neither can the autopilot so it won't be on. If the pilot put the plane on autopilot and then ejected, the ejection would most likely force the autopilot to disengage. If a pilot put a plane on autopilot, walked into the back of the plane and opened a door and parachuted out, the plane would continue flying on autopilot until it ran out of gas and then the autopilot would disengage and the plane would crash.

I don't think autopilot programs are anywhere close to that complex. All the ones I've seen had modes like "hold course and speed" or "follow a series of pre-programmed waypoints". Some military aircraft will have a radar guided terrain following mode as well. In the (highly unlikely) event that the autopilot is engaged when the pilot ejects, the autopilot is just going to continue following whatever mode it's set to.

My kids ask questions like this all the time.

Them: What if a shark jumped into a volcano?

Me: That wouldn't happen because sharks live in the ocean and can't jump high enough or far enough to reach land.

Them: OK, but what if?

Me: ... It would get burned and die...

So yes, if a pilot ejects and the plane had auto-pilot on and the auto-pilot was programmed to try to land after a pilot ejection and the plane was still safe to fly, the plane would in fact attempt to land.

The assumption inherent in the question is that there is some kind of autopilot mode or logic change based on whether ejection has occurred or not. It is pretty unlikely that such explicit logic exists.

Also, ejection only makes sense in the context of a manned military aircraft. For the question to make sense as posed, the implication is that the pilot had engaged the autopilot and then ejected while the autopilot had meaningful control authority over the aircraft. That's not a scenario the airworthiness certification authorities probably consider as critical. Manned aircraft require deliberate human action to engage the autopilot. What the flight control computers do in general (e.g., limit control inputs to keep aircraft within acceleration/maneuvering limits, automatically enter a stable attitude when stick forces are not present) is not considered the "autopilot".

You could ask the question, "If the pilot ejects, do flight control computers attempt to fly the aircraft in any particular way?" At least for U.S. aircraft, recent ejections (e.g. the Thunderbird ejection near the end of Obama's tenure), suggest the answer is "no". If an automated flight termination system is installed, when safety constraints are violated (e.g., heartbeat signal or veering outside of geographic limits) it usually takes action to put the aircraft into the ground as quickly as possible (e.g., cut power to actuators on an unstable aircraft). This is common with UAVs. I don't think this is the case with manned aircraft.

Welcome to stackoverflow- where avoiding the question is an art.

That wasn't the autopilot though, that was just aerodynamics.

fantastic, i love anecdotes like these.

Re: Mig-23 incident - at the time of the incident it was a popular theory that this was Soviet's answer to Mathias Rust landing his Cessna on Red Square two years prior.

https://en.wikipedia.org/wiki/Mathias_Rust

Even moreso, I would expect that with most experimental or non-commodity military craft in actual combat situations (i.e. the kinds you really don't want the enemy analyzing or using against you), the plane would just explode as soon as you're a safe distance away.

Like scuttling a ship, but smaller.

For enemy recovery reasons?

I suspect it's fine. Two-seater planes fire the seats in sequence - if it's not frying the other passenger, it's highly unlikely to be melting the instruments.

https://upload.wikimedia.org/wikipedia/commons/9/9c/Ejection...

As someone who has worked on the F/A-18 (actually CF-18) mission computer software, when the pilot ejects the mission computers start to erase the sensitive information that they contain.

I think that's a very valid objection.

However, you could ask a similar question with a modified premise: you'd want to build in a way to have control over the fate of the airplane.

Depending on the situation, the right thing might be to safely land it (if in friendly territory), destroy it as thoroughly as possible (if in hostile territory), or protect lives on the ground (if you don't think you can land it).

But whatever the goal may be, maybe the autopilot could do better than leaving it to chance.

EDIT: I forgot about a fourth possibility. If in hostile territory, maybe use the autopilot to turn the plane into a weapon. You're leaking fuel so fast there's no way you'll make it back to base, but maybe you still have enough fuel to pick up a lot of speed before slamming into a nearby enemy asset.

Which isn't an answer to the question.

"The autopilot doesn't change its operational parameters to account for ejection." would be an answer, meaning it takes no account of it and continues as before.

Saying "it's programmed to do nothing" is very different: meaning it would stop, meaning it would be taking notice of the ejection.

I prefer TL;DRs that give at least _some_ insight. In this case, the answer is short enough to not need a TL;DR.

The autopilots flight envelope limits are somewhat artificial though. If you wanted to, you could design it to try and take over no-matter-what in the event of an ejection.

The biggest question I'd have is: What would you even want the auto-pilot to try and do after an ejection? Assuming it somehow gained full flight control, then what?

You've answered a different question.

They didn't ask would it be likely in an ejection event, they asked what the programming parameters were.

AFAICT it's "continue as before", which is useful to guide the aircraft away to avoid excessive harm to people/property.