James is correct about the timing of the flights. And I sympathize with my sister for not wanting to hang around to find out if they would put her on the first flight out the next morning for several reasons.

First: this was a weekend trip meaning she was returning to New York on a Monday flight. If she were to get on a Saturday flight she wouldn't arrive till 9pm London, giving her all of 36 hours in town.

Second: "messing with the situation" takes on a whole new meaning at JFK on a rainy Friday night and a 747 full of people have just been cancelled out of their flight at 1130pm. Given the circumstances of the trip I don't know why anyone would hang around for several hours at JFK to sort it out when it's a mechanical failure on the part of the airline. Mind you there were no announcements whatsoever about the guarantee of seats on another aircraft, etc.

Third: this was a mechanical failure on the part of the airline.

I guess I should have posed my question a little more generally. On domestic flights I know of Rule 240 and our rights to demand to be delivered to our destination within 4 hours of scheduled arrival. We can also get compensation in those situations.

What is the situation for international flights? Is it totally up to the ailine involved? Or are there some sort of similar rules?