Missing plane: when something went wrong
The process of unravelling what really happened to missing passenger jet MH370 boils down to a crucial 30-minute window, during which something on board went horribly wrong.
It was between 1.07am and 1.37am local time on March 8 that the Malaysia Airlines plane, with 239 passengers on board, appeared to vanish into radar darkness and deviated from its intended path.
Whether that was an intentional action by someone on board the plane, human error, or down to a mechanical fault, relies on investigators forensically reconstructing the 30-minute block shortly after the plane took off. Such a task would seem to be nearly impossible without recovering the plane's flight data recorders.
What the investigators do know is this.
When the Boeing 777 took off from the Malaysian capital Kuala Lumpur en route to Beijing at 12.41am on that Saturday morning, all of the tracking systems on the plane were working as normal.
At 1.07am, the plane's Aircraft Communications Addressing and Reporting System (ACARS) automatically transmitted flight data to the ground. The ACARS system collects detailed information about the plane's and the pilots' performance and automatically transmits details via satellite to the airline, engine manufacturer and ground controllers every 30 minutes.
The next transmission from MH370 was due at 1.37am. It never occurred.
It was within this 30-minute window - at precisely 1.19am - that a male voice now identified to be the co-pilot, Fariq Abdul Hamid, spoke the last known words from the cockpit to ground control.
"All right, good night," Fariq said, sounding nonchalant and giving no indication that anything was amiss.
The words were transmitted as the plane passed from Malaysian airspace into Vietnamese airspace, and Fariq's words are said to be radio parlance used by pilots in such circumstances.
Just two minutes after this communication - at 1.21am - the transponder on the plane ceased working.
The transponder is a second communications system that automatically sends electronic messages, or ''squawks'', to radar systems about the plane's altitude, flight number, speed and the direction in which it is heading.
Investigators in Malaysia appear to be stumbling as they try to piece together this crucial 30 minutes in the chronology of the flight.
On Sunday, Defence Minister Hishammuddin Hussein, who is also Malaysia's acting minister of transportation, said that the ACARS system had been disabled at 1.07am.
That pointed to the possible complicity of the pilots in the plane's disappearance, as Fariq's verbal communication 12 minutes later gave no indication anything was wrong.
But just a day later, Malaysia Airlines CEO Ahmad Jauhari Yahya clarified that the last ACARS transmission was sent at 1.07am.
Therefore, the ACARS was shut down sometime between 1.07am and 1.37am, and Fariq's final voice transmission may have occurred before any of the jet's communications systems were disabled, he said.
"We don't know when the ACARS system was switched off," he said.
The new description of what happened to the ACARS system appeared to reopen the possibility that the aircraft was operating normally until the transponder ceased sending signals two minutes after the last radio message.
The transponder box is located in the cockpit, within reach of the pilot and co-pilot, said Kirk Fryar, president of Sarasota Avionics, which sells the devices.
He told CNN that transponders were equipped with an on, stand-by or off mode.
Switching off the ACARS system, however, is a much more complicated task and would require considerable expertise. The only way to disable it is by pulling a circuit breaker in the cockpit.
Malaysian Prime Minister Najib Raza revealed at the weekend that a satellite tracked the plane at 8.11am, more than seven hours after take-off.
He did not provide any details on the satellite tracking, however aviation experts have said orbiters high above the ocean may have detected the plane as the satellite or satellites attempted a series of "handshakes" - or electronic connections - with the plane below.
Meantime, if the plane was deliberately diverted, passengers on board MH370 may have had no idea that anything was wrong.
It was a red-eye flight from Kuala Lumpur to Beijing, and many passengers presumably would try to sleep during the night flight.
Window shades would have been down and it would be night outside, with no sun for passengers to potentially track the plane's change in direction.
The change in direction also appeared to take place between Malaysian and Vietnamese air space, potentially creating some confusion between who was communicating with the plane.
Sydney Morning Herald