That was my first thought, but it was being tracked on radar at 30,000 ft. I do not believe a 777 can dive fast enough to disappear in background clutter over open ocean before the next sweep or pulse and still pull out and survive. Therefore the most likely explanation is not that it disappeared, but rather that it became scattered into parts too small to be tracked from that distance. Assuming the Romulans didn't swoop down and get it.
Anyone know the particulars of the radar tracking it?
I'm pretty sure that in this case, the plane was out of primary radar range, which is ground based radar. Primary radar tends to stop a bit far out from the cost.
The plane location is broadcast by secondary radar, the aircraft transponder system which continually broadcasts its location/altitude/speed etc etc etc.
The worrisome thing in this case is that secondary radar is not supposed to simply fail unless power is completely cut to it.
This can mean several things
1) Fire sprang out on board that cut the main power lines to the system. Unlikely because that fire would have had to spread extremely quickly to do so, and a mayday probably would have been issued.
2) Bomb severed the main connections. More plausible, and in my opinion probably the most likely cause, but that's complete conjecture. Though it would explain the lack of maydays or distress call.
3) Hijackers turned it off in the cockpit. Personally think this is shenanigans. Even if the hijackers somehow managed to get access into the locked cockpit without the pilots issuing a radio warning, where the hell are they going to go? A 777 is a big plan and everyone is looking for it.
4) Engine failure. The engine powers the transponder, and in event of total power loss, the backups do not power the transponder because all emergency power is dedicated to keeping the plane afloat. However, I do believe the radio stays on, which is why this isn't plausible.