The Transponder Mystery
The transponder was off when the plane 'vanished', but it is unlikely that the system may shut down by itself. John Goglia, a former member of the National Transportation Safety Board said that a transponder cannot shut off by itself, especially when a knob in the cockpit has to be turned off, along with various other switches that need to be shut off manually. This can be done only by the pilot or somebody who has researched the plane on the internet.
The system encountering a technical problem can be ruled out as the last contact by the very experienced pilot did not mention any trouble.
The Flight was Guided
With the transponders off and with no contact with the civilian radar, it is next to impossible for an aircraft to stay on track. Interestingly, the Malaysian Airline was very much on track, though heading west. This, in fact has been noted by the Malaysian military radar, which kept on receiving the blips till the plane went beyond its range.
Also, the plane was then tracked along a known flight route across the peninsula. Airliners normally fly on specific routes that can be monitored by air traffic controllers who space them out to avoid collision. These lanes aren't straight lines and to follow them, the plane has to be guided.
The fact that the plane was flying erratically can be ruled out as it was well within the range of military radar, which displayed steep ascents to very high altitudes and then sudden rapid descents. Surprisingly, without a transponder on, it is impossible to track planes at very high altitudes or on erratic altitude shifts.
The ACARS theory
Surprisingly, the Aircraft Communications Addressing and Reporting System (ACARS) was shut off, which only a pilot can do. The system has two parts, investigators say-one part is used to send short messages through a satellite or VHF radio to the home base. The second part, however, just transmits signals to the satellite, making itself visible to the military radars.
Interestingly, the information part was switched off and not the transmission part. Experts say that the information part can be switched off by hitting the cockpit switches in a particular order to get to a computer screen where one has to select an option using a keypad.
However, it is not easy to switch off the transmitter part of the ACARS as the pilot does not know how to do it. It requires going to an electronic bay beneath the cockpit, which was not done in this case. The ACARS transmitter, hence, sent out blips to the Inmarsat satellite, once in four to five hours, after the transponder was shut off.
Though the blips do not have any information in them, they can help locate the aircraft. Furthermore, the satellite adjusts its satellite's antenna to receive messages from the ACARS, if sent.
Investigators are now analysing these blips and the last reading before they stopped completely.