How does an aircraft report crew programming of the FMS to the ground? [closed]

I am reading in the news that the MH370 flight changed its course by "Computer entry" and that it was programmed into the computer at least 12 minutes before the last voice contact with the plane.

How can they know that the change in the computer was done 12 minutes before (while the plane was still flying as on the original course)? And how do they know it was done in the computer, rather than the pilot steering manually?

The aircraft's Flight Management System (FMS) can be loaded with software that periodically sends position reports and flight tracking data to ground stations via ACARS. If the particular software in use sends the full flight plan or at least the next few fixes periodically with estimated times, this would expose any changes in the flight plan to the dispatch office.

The incident flight in question had its ACARS turned off at some point and the "12 minute" figure is probably derived from the time between the last ACARS message being received and the radar observed turn off course initiated. They would not be able to know exactly when the buttons on the FMS were pressed, but they could narrow the time down to a range when information changed between two automated reports sent via ACARS.

Relevant chronology:

01:07 final ACARS transmission
01:19 final voice communication


Interval: 12 minutes.

• My guess is the "reporter" didn't know what they were reporting. As far as I know you don't need the FMS to change the heading the autopilot uses. The autopilot can be controlled by the FMS but the autopilot can be used independently. – rheitzman Mar 20 '14 at 21:38
• @rheitzman it is true you can change heading with the autopilot alone but if you are flying a course 99% of us will put the fixes into the FMS for the autopilot to fly. – casey Mar 20 '14 at 22:25

The earlier report referred to in the question has been contradicted by a later report. This undermines the premise of the question. Currently (24/3/2014) it appears there is no evidence that any change in flight-path was entered into the flight management system.

Malaysian officials, in a written update Sunday on the search, cast doubt on the theory that someone, perhaps a pilot, had reprogrammed the aircraft to make an unexpected left turn during the flight.

"The last ACARS transmission, sent at 1:07 a.m., showed nothing unusual. The 1:07 a.m. transmission showed a normal routing all the way to Beijing," it read.

• CNN March 24, 2014 at 0225 GMT