Alien abduction Sophisticated kidnap?
Still doesn't answer where is the plane and how can a plane just fly around the skies with no one "noticing" or intercepting with military jet.
Are air crews luggage subject to security checks like the passengers? If the crew hijacked their own plane how did they subdue the passengers? Otherwise the minute they landed or had to leave the cockpit the passengers would overcome them.
Without a transponder signal the aircraft is invisible to everything except local radar (just a blip on a screen) and the naked eye (it was dark, so reasonbable to assume that they also turned the lights off). If it's not near anything sensitive, no one would really raise an eyebrow, and being dark it becomes a hole in the sky.
The passengers were on a six hour night flight, the first sign of an issue would be when they landed and couldn't get off the plane.
The crew all go through the same security checks as any passenger or airport worker, the more complicated you make summat, the more likely you are to get caught. Equally the more people in the loop, the more chance of an information leak.
Based on what is known... this is how I would have done it...
1.Transponder, exterior lights off.
2. Flight deck full face oxygen masks on. (cockpit has plumbed in long term oxygen supply).
3. Reduce cabin pressure from 10,000ft to say 2-3000, whilst simultaneously climbing to 40-45,000ft. This would purge the breathable atmosphere from the cabin, incapacitating the passengers/crew. (An alternative would be drugging the meals during the meal service but given the time of the flight, first meal was probably breakfast...)
4. Return to a flight level low enough to enable visual navigation, but not so low as to be suspicious and critically a flight level not full of aircraft, say 20-25,000 ft
5. Fly to a destination of my choice, possibly Pakistan.
If I were a suicidal type, I would bin it somewhere loud and obvious, much like the EgyptAir pilot in '99.
If I were a simple terrorist, I would want the bang to be devastating and again loud and obvious.
If I were a hijacker, I would order the plane to land somewhere and have a long list of demands, again loud and obvious.
If I were a believer in a cause, I would take control of the aircraft, incapacitate the passengers and deliver the aircraft to an Al Qaeda camp in northern Pakistan for them to use it as they will.
If they don't find the wreckage, the next time that aircraft is spotted will be too late...
By the time the authorities start to think a bit beyond their noses, the aircraft will probably be back in the air, and on it's way to it's final destination. My guess on this would be the US east coast via Africa.
Although the ACARS
was transmitting a basic signal that could be disabled on the ground easily enough. The transponder could easily be switched with one from an aircraft with similar speed capability (basically any twin engine jet from a Learjet up). It would then be free to fly anywhere on a legitimate private flight plan, and by flying at night, it would never be spotted. Could literally get anywhere.
Think stealing a car, waiting a week to see if it has a tracker fitted, then change the plates and off you go...