One variant of a scenario geoffb linked above might explain the lack of passenger participation (using their cell phones or other devices to attempt to establish post-takeover communications). If induced gradual oxygen deprivation via non-explosive cabin depressurization was employed by one or more hijackers who had oxygen masks, then all the passengers would be conveniently dead soonest. Re-establishing cabin pressurization would allow the hijacker(s) to collect and destroy communication-capable devices.
That variant would also explain the rambling flight patterns between the checkpoints: the pilot furiously searching passengers and their carry-ons for devices.
(The pilot - hijacker(s) disabled the aircraft's telemetry equipment, then diverted it well out of it's intended path; likely to prevent any tracking, or the finding the wreckage and thereby have the good guys working to solve the mystery: whodunnit? Who gets bombed to glass this time?)
But they missed disabling the data pings from the engines or other on-board sources. Perhaps they weren’t aware they even pinged.
My best guess is that the hijacker(s) learned much from the Lockerbie failure.
The Pan Am Flight 103 Lockerbie explosion was intended to take place over the ocean, making wreckage recovery and subsequent identification of the responsible party impossible; but instead, it happened over Scotland. That led to the subsequent bombing of Gaddafi's Libya, and the killing of his daughter. So, lesson learned, that wasn't going to happen again.
If the scenario I postulated above happened, after all devices were rendered inoperable, the jet's fuel near-exhausted, the plane was then pointed straight down and accelerated to eleven. That would account for the the 40,000-foot drop in less than a minute, as was reported by the engines.
Is there a deep trench in the Indian Ocean? That’s where they needs search.
Oh. Sunda Trench...
...is located in the northeastern Indian Ocean, with a length of 2,600 kilometres (8,500,000 ft). The maximum depth of 7,725 metres (25,344 ft) (at 10°19′S, 109°58′E, about 320 km south of Yogyakarta), is the deepest point in the Indian Ocean. The trench stretches from the Lesser Sunda Islands past Java, around the southern coast of Sumatra on to the Andaman islands...Andaman islands, you say?
The suggestion -- and it's only that at this point -- is based on analysis of radar data revealed Friday by Reuters suggesting that the plane wasn't just blindly flying northwest from Malaysia. Reuters, citing unidentified sources familiar with the investigation, reported that whoever was piloting the vanished jet was following navigational waypoints that would have taken the plane over the Andaman Islands.If the hijacker(s) intended to escape the Pan Am Flight 103 - Lockerbie scenario, they would put the plane out of reach of searchers. Deep and forgotten.
The radar data don't show the plane over the Andaman Islands, but only on a known route that would take it there, Reuters cited its sources as saying.
“Dastardly pings! Curses, foiled again!”
Iran hardest hit.