What's remarkable is how long the airplane, after abandoning the ATC network, continued to ping Inmarsat. Inmarsat was never designed to track airplanes, but, nevertheless, the Inmarsat engineers were able to tease out enough info from their logs to establish that the airplane headed south and west until it ran out of fuel. Their conclusions as to the flight path were what established the search area – in the Indian Ocean southwest of Australia.
Then there is the intriguing fact that the copilot's cell phone logged in briefly after MH370 ditched ATC but before it had flown out of range of Malaysian cell towers. Why was his phone turned on? Was he locked out of the cockpit?