Aerospace engineers, how long would a commercial passenger aeroplane last in the vacuum of space, before it starts leaking atmosphere?

I’m not a “structural” guy . Maybe someone can answer that part of your question.
I can however answer about over design.
We make an engine critical part that is exposed to an operating pressure of 200 PSI, 400 PSI peak. We designed the part to withstand 5000 PSI and cycle pressure test it to 3000 PSI at elevated temperatures. (Sorry about the units but those are the specs.)

I doubt the structure can be so heavily over-designed. It would never get off the ground.

Te ambient pressure at 35,000 ft is approx 0.25 bar. It is conceivable that a craft designed for that altitude craft could survive in outer space since that would be only about 33% more stress.

Airliners have pressure relief valves that will vent air anytime the inside/outside pressure differential exceeds the design limits of the fuselage. So these would immediately begin venting if the aircraft were in a vacuum.

@thorninmud Design limits often have a safety margin in them though, so I see it as a valid question.

However, I think that the fact that there are unpressurized cargo holds would be a bigger issue as I somehow doubt the internal compartmentalization barriers are nearly as rugged as the outer hull. It seems to me that you’d blow out interior bulkheads first were it not for relief valves.

Aircraft are dependent on air to fly. Spacecraft are designed to operate in a near vacuum. I am not an engineer, however.

I suspect a lot would depend on how quickly the aircraft is subjected to near-vacuum.

Since, as @Bill1939 notes, aircraft aren’t going to get to space by any normal means, this is a completely hypothetical situation.
If the craft is subjected to slowly reducing pressure it would likely not experience catastrophic structural failure – although any occupants will probably die from insufficient air.

If it’s suddenly subject to the near-vacuum then it could well pop.

I’ve been thinking about this since you asked. Let’s ignore how the plane got up there. That part is impossible. Let’s just say it is there.

I’m going to make a bold prediction: The plane will survive – but with shortened life.
Here’s why I think so.
When we run a durability test on a shaker we accelerate the testing by doubling the vibration level forces. Every doubling of the g levels shortens the testing one decade. For example a 2000 hour test can be shortened to 200 hours by doubling the g level. Double it again (4 times the nominal) and the test will be shortened to 20 hours.

Consider the pressure change of every flight, 1 atmosphere to 0.25 atmospheres, and back every take off and landing. Let’s say a plane has a life of 10000 TO&L. By doubling the pressure difference for each cycle: 1 atm to -0.5 atm (impossible) we will get a life of only 1000 TO&L. Since we can only go to 0 atm in space, the difference is an additional 33% so the durability test acceleration factor will be ~ 0.5 or about 5000 TO&L.

Yes. The plane and the people will survive – until they use up the oxygen on board.

If the craft is in orbit, would the passenger still collect their 25,000 frequent flier miles every 90 minute orbit?

Actually, it is possible for the plane to get up there. Of course, it’d take a bit of speed and there is a portion of the flight path where neither the control surfaces nor the engines will work due to lack of air. This sort of semi-ballisitic flight is generally reserved for missiles, though the X-20 has done it and proposed SpaceLiner will do it.

@jerv. There is no way it can get up there by itself. The jet engines can’t do it. The planes top out at 600 -700 mph. They need to hit 17,000 mph to reach orbit. Look at the size of the engines and booster that lift the space shuttle to orbit. And the shuttle rides on the back of a 747! Imagine how big they wold need to be to lift a 747. Wow!

@LuckyGuy Yes, putting something in orbit takes a lot more than just lobbing it in an arc, but who said anything about going into orbit? If you intend for whatever you launch to come back down within a couple of hours (a good amount of time for a commercial passenger flight), you can get away with far lower speeds.

@jerv. If you want something to go up and stay up more than 90 minutes you have to put it in orbit or else you need to pack a tremendous amount of fuel to keep it up. And then it will only stay up until you run out of juice. What goes up, must come down – unless you put it in geostationary orbit. :-)

@LuckyGuy Who wants a flight from NYC to London to take days or weeks though? I mean, coming down (preferably without Lithobraking) is kind of the point.

You do not need a geosynchronous orbit to stay in space. Just have an apoapsis outside of the atmosphere, then circularise your orbit. Works for Kerbals, at least.