Originally Posted by Derek

So it was either diverted to an isolated airfield which would need:

• An isolated airfield with the associated workers to all remain quiet
• The crew on board to be in on it. Or the passengers that were hijackers to be so good at hijacking that they could seize the plane without a whisper leaking out
• Multiple countries faking or losing radar data
• Inmarsat faking their data, then releasing it to let everyone see how clever they were at faking it
• All the countries the plane overflew not seeing anything
• A way to get rid of a few hundred bodies
• A way to hide a large aircraft
• And most importantly, a reason for hijacking the plane and then not making any demands whatsoever

Or possibly a single person (pilot / co-pilot) diverted it to the middle of the ocean in a suicide bid.

Yep the hijacking by the black helicopter brigade sounds far more plausible.