Originally Posted by
MSPeconomist
After three hours, passengers generally must be permitted to deplane or the USA DOT can impose heavy fines on the operating carrier.
In some cases, the airline announces that you can leave the aircraft but then you will/may not be ablle to get back on it if the flight is going to depart.
IIRC there are also some vague comfort requirements, such as water, AC/heat, functioning lavatories, etc.
However this was an international flight and according to this DOT
link, it's up to the airline to specify the length of time. I took a quick look and it seems that AA has committed to doing something after 2 hours.
AA.com.
I presume that's for both domestic and international but in any case, the weather would probably present a safety issue allowing them to keep pax on the aircraft longer.