Malaysian authorities have rekindled confusion over the sequence of events on board the missing Malaysia Airlines Boeing 777-200, with apparently differing accounts of the status of the ACARS messaging system.

Prime minister Najib Razak had stated on 15 March that, based on satellite information, investigators could say “with a high degree of certainty” that ACARS was “disabled” just before flight MH370 reached the east coast of the Malay peninsula.

The aircraft crossed the coast, southeast of Kota Bharu, at around 01:07 on 8 March. This is also the time at which ACARS transmitted its final message.

Malaysia’s acting transport minister, Hishammuddin Hussein, told a press conference on 17 March that he could “confirm” that the ACARS system was “turned off just off Kota Bharu”, while the transponder was deactivated at the IGARI waypoint.

MH370 search map

But Malaysia Airlines chief Ahmad Jauhari Yahya appeared to contradict both accounts shortly after Hussein’s comments.

While he confirmed the last ACARS transmission occurred at 01:07, he said: “We don’t know when the ACARS was switched off after that.”

He says the system was supposed to send another transmission 30min later. “But that transmission did not come through.”

This means ACARS could have been switched off any time over that subsequent 30min period, he says.

The inquiry revealed that the final voice communication from the crew – a routine sign-off to air traffic control, probably from the first officer – followed at 01:19.

Timing of crucial events has previously been cloudy. Department of Civil Aviation director general Azharuddin Abdul Rahman had said, on 12 March, that the flight had been “coasting” on secondary radar at about 01:21, but then added that the target “disappears altogether” at 01:30, without clarifying the surveillance situation in the intervening 9min.

Web-based flight-tracking software, while not an official source of data, indicates a loss of transponder information at about 01:21.

Civil primary radar could not pick it up at this point, but analysis of military primary radar indicated a possible turnback by the aircraft. This analysis, and the identification of a primary radar target off the western coast of the Malay peninsula some 45min later, subsequently led to the expansion of the search.

Source: Cirium Dashboard