Investigating authorities have yet to detail the missing Malaysia Airlines Boeing 777’s track following its loss of contact, and indicate whether any evidence supports the course being amended via the flight-management system.
Acting Malaysian transport minister Hishammuddin Hussein told a press conference on 19 March that the aircraft “flew on normal routing” until it reached the IGARI waypoint.
Hishammuddin had been attempting to address media speculation that additional waypoints had been inserted into the aircraft’s route.
He stated that there was “no additional waypoint” on flight MH370’s “documented flight plan” which depicted the normal track from Kuala Lumpur to Beijing.
Hishammuddin did not clarify whether he was referring to the flight plan initially filed for MH370 before its departure on 8 March, or whether the inquiry had no evidence of subsequent amendment.
While MH370 was being tracked on secondary surveillance radar, the probe has not indicated the status of other potential surveillance.
The aircraft was equipped for ADS-B, through which its transponder automatically broadcasts position data on a regular basis.
But it would also have been capable of ADS-C, a datalink application under which the aircraft is specifically contracted to transmit certain flight information over the ACARS communication system.
Depending on the contract the transmissions can be initiated by particular events – such as the inclusion of a new waypoint entered by the flight crew, for operational purposes, or a deviation from altitude and airspeed expectations.
The inquiry has not stated whether MH370 was subject to an ADS-C contract.
Investigators have not given full details of the ACARS transmissions received by the aircraft, the last of which was received at 01:07, about 14min before the loss of transponder signals.
MH370 disappeared in the vicinity of the IGARI waypoint located just before the Singaporean-Vietnamese airspace boundary, the point at which the aircraft would have crossed into the Ho Chi Minh flight information region.
Investigators state that the aircraft did not begin to divert from its course before the final voice communication, a sign-off message, was transmitted to air traffic control.
Although the 777’s transponder and ACARS data were lost, military primary radar subsequently recorded a westbound target which the inquiry identified as the missing jet. Full details of the radar plot have not been disclosed, and the investigation has not confirmed whether it coincides with defined waypoints.