If we assume that there is some level of outside planning here, with maybe a state actor involved, then getting the plane secretly fuelled up beyond the assumed 7.5 hour range would perhaps not be too difficult.

What are the odds that if you had that plane, you could 'sneak in' to US airspace and pull another 9/11?

Trust me, you can get an aircraft with enough range to get anywhere in the world in a couple of hops for much less than the cost of organizing a highly sophisticated hijacking operation. And your range is much longer when your aircraft is operated by an apparently legitimate charter service that has permission to fly into most countries and don't have to worry about hiding from radar.

By contrast, the effective range of a suspicious phantom plane against fighter jets on high alert is zero.