But if passengers all got off en masse do you think they would all have been arrested?
Airside at an airport is a secure, contained* area. They would all have been arrested.
*in most cases. You could make a swim for it from London City, but you'd end up very wet and the local police could get to the other side before you even if they didn't dispatch the rescue boat to come and get you.
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Back to the railways though. On the occasions I have been on a train that's gone nowhere for a signficant length of time, almost all have been at stations. E.g. Last September, signalling failures on the Brighton Mainline meant we were stuck at Haywards Heath for about 45 minutes, but the driver explained what was happening and opened the doors to let us on and off as we chose although most people stayed on board. I happened to overhear the driver complaining to a member of station staff that he was meant to be a Brighton Express but could be prosecuted under the trade descriptions act (we pulled into Haywards Heath about 20 minutes later than we should have been passing through iirc).
Circa 2009 I was on a DMU heading from Bristol Temple Meads towards Weston-super-Mare. North of Nailsea and Backwell the guard was at least verbally assaulted* by a passenger who did not have a ticket and retreated to the rear cab (I was travelling in the rear car). The train came to a stop a few moments later and then after a few minutes the driver came striding through the train and spent a good 10-15 minutes in the rear cab with the guard. Eventually we did get on the move again to Nailsea & Backwell but the doors were not released for another ~10 minutes until the BTP arrived. I don't recall any communication but at least in the carriage I was in we had all to some-extent witnessed what had happened and there was no problems beyond muttering. Apparently though, despite this being a pretty much full service I was the only one who was prepared to give my details and a full statement to the BTP.
*The BTP said he claimed to have been physically assaulted, and his reaction was consistent with this, but I didn't actually see anything other than a verbal assault from where I was sat.
Most relevant perhaps was on a London-bound FGW HST where we stopped somewhere east of Slough "due to a bit of metal making a lot of noise beneath coach C" (I was in coach A and so wasn't aware of anything but clearly remember the explanation given). After what felt like about 20-30 minutes stationary we pulled into West Drayton ("waiting for a fitter to arrive from Swindon" or words to that effect) yet still it was a good 20-30 minutes before the doors were released and we all overloaded an all-station service to Paddington (I can't remember if it was Thames Trains or FGWL, definitely pre FGW operating the locals) and I think that might have been a reaction to (threatened) self-evacuate.
The bottom line, from a passenger point of view, is that if you keep us locked on a train without telling us why, then sooner or later we will self-evacuate. How long you have depends on the proximity of a station (any station) - if all or part of the train is in a platform you probably only have 20 minutes at most unless there is a reason obvious to a passenger who knows nothing about railways. If the train is not in a platform but we can see one or enough passengers know there is one just round the corner, you probably have 45-60 minutes tops. If we can't see a station then you've probably got 1-2 hours.
If you do tell us why you just buy yourself time. How much extra time depends on how good the reason sounds to someone who doesn't know anything about railways.
