Malaysia Airlines Flight 370 satellite communications

The analysis of communications between Malaysia Airlines Flight 370 and Inmarsat's satellite telecommunication network provide the primary source of information about Flight 370's location and possible in-flight events after it disappeared from military radar coverage at 02:22 Malaysia Standard Time (MYT) on 8 March 2014 (17:22 UTC, 7 March), one hour after communication with air traffic control ended and the aircraft departed from its planned flight path while over the South China Sea.

Flight 370 was a scheduled commercial flight with 227 passengers and 12 crew which departed Kuala Lumpur, Malaysia, at 0:41 MYT (16:41 UTC, 7 March) and was scheduled to land in Beijing, China, at 6:30 China Standard Time (6:30 MYT; 22:30 UTC, 7 March). Malaysia has worked in conjunction with the Australian Transport Safety Bureau to co-ordinate the analysis, which has also involved the UK's Air Accidents Investigation Branch, Inmarsat, and US National Transportation Safety Board. Other groups have also made efforts to analyse the satellite communications, albeit challenged by a lack of publicly available information for several months after the disappearance. On 29 July 2015, debris was discovered on Réunion Island which was later confirmed to have come from Flight 370; it is the first physical evidence that Flight 370 ended in the Indian Ocean.

During flight, the aircraft maintains a datalink with a satellite communication network for data and telephone calls. The datalink connects the aircraft and a ground station via satellite, which translates (changes) the signal's frequency and amplifies the signal; the ground station is connected to telecommunication networks which allows messages to be sent to and received from other locations, such as the airline's operations centre. Normal communications from Flight 370 were last made at 1:07 MYT. The datalink between the aircraft and satellite telecommunication network was lost at some point between 1:07 and 2:03, when the aircraft did not acknowledge a message sent from the ground station. Three minutes after the aircraft left the range of radar coverage—at 2:25—the aircraft's satellite data unit (SDU) transmitted a log-on message, which investigators believe occurred when the SDU restarted after a power interruption. Between the 2:25 message and 8:19, the SDU acknowledged two ground-to-aircraft telephone calls, which were not answered, and responded to automated, hourly requests from the ground station that were made to determine whether the SDU was still active.