What could have happened to the flight?
Sudden depressurisation, caused for example by a window blowing out, a door coming open, or a failure of some part of the pressurisation system. All of these events have happened before. With a sudden depressurisation at 35000', the pilots would have around 7-10 seconds of useful consciousness to get their oxygen masks on, and, provided no catastrophic structural damage has occurred, they should be able to continue to fly the aircraft.
Unlawful interference. Flightdeck doors these days are armoured but their effectiveness depends on the crew using the correct protocols for opening the door for routine events (meal service & toilet visits).
Inadvertent thrust reverser deployment. e.g. as happened to
Lauda Air 767 in 1991. A very bad thing to happen and virtually unrecoverable if it happens at cruising speed, as this aircraft would be after 2 hours of flight time.
Which systems report the aircrafts position routinely?
Voice radio. Needs a live pilot to activate it.
Ground based primary radar. Not sure if the area where the aircraft was supposed to be was covered by this system.
Secondary radar. A ground based system interrogates the aircrafts transponder which reports back position, altitude, heading, and speed data. Can be switched off on the flight deck but there are no normal circumstances when this would occur.
Some large airlines use a system called ACARS to communicate with their aircraft. Some ACARS systems (like on the B777) can be used to feed live telemetry back to the airline HQ so they can monitor engine data for maintenance purposes. I'm 99% certain that position data would be reported also. I'm not certain if Malaysian used this facility.
Which systems report position data in an emergency?
Both the Cockpit Voice Recorder and Flight Data Recorder have radios which start to transmit a signal certain parameters (sudden deceleration, loss of power supply, etc). All the search aircraft and ships will be listening out on the appropriate frequencies to pick up these signals and home in on their location.
Passenger aircraft are required to carry portable Emergency Locator Transmitters. If the aircraft crash lands in a remote location, the ELT may be activated automatically or manually and carried by survivors if they leave the crash location.
It seems to me that as well as something non normal happening to the aircraft, the ground based monitoring, both from ATC and the airline appears to be non normal also.
It doesn't look good for the passengers, crew and relatives.
