I don't think think they'd keep it, then crash it. They'd have to keep the hostages alive to use them as protection, prepare the plane refuel the plane some how get it to take off from one of the little islands it's on etc If they were going to crash it into something, they wouldn't have waited a week or perhaps months for the search etc to die down. They'd have just done it straight away. I imagine if they had planned all of this shit they'd have gone fuck it I can find an abandoned airbase with plenty of planes to use where nobody would notice they were missing so no guards and security would be stepped up etc. I can't see them stealing a plane knowing it would be publicised for them to have to hide it etc. unless there was someone or something of value on it