Simply put is the work of terrorists.

Could it be the 2 Iranians maybe.

Could it be made to look like the 2 Iranians.

I believe

They hijacked the plan, disabled the transmitter, flew it low to get off radar over water.

Landed somewhere with Muslim extremist and have plans for the hostages and the plane at a later date.

Since 9-11 I suspect the planes are always a target getting your hands on a flying bomb and one that now has disappeared make it all the more interesting.

Or something bad happened and the governments are covering up their mistake.