There is one other largely unknown example of an airliner disappearing. This one was a good condition ex American Airlines jet that was chartered to central Africa. The pilot and mechanic was then "persuaded" to stay on for quite some time (months), rather than immediately return as was the plan, flying the plane for the new operators. Of course, it was allowed to deteriorate ridiculously. Then, after sitting on a ramp collecting dust (and weeds), someone, they aren't sure who, came along and started getting it back to flyable (note I did not say "legally airworthy") condition. One day, it fired up its engines, taxied to the end of the runway, took off without clearance, and disappeared to the west over the South Atlantic. A search of the pilot's movements turned him up missing, with little if any evidence that he was at all involved in the disappearance of the aircraft. The original charter owner (in the southern US as I recall) claimed (and I believe got) the insurance for the aircraft, and that was that. It hasn't been seen since. The restructuring of the aircraft as a "tanker" with massive internal fuel bladders that were, as I recall fed into the fuel system, mean that the thing had a ridiculous range, at least in theory. That meant that despite being a short range 727 in theory, in practice, it could fly the Atlantic in one go, something that troubled the US, thinking it could be used in another attack.
http://en.wikipedia.org/wiki/N844AA