Loss of contact

Flight MH370: Loss of Contact

Malaysia Airlines flight MH370 departed Kuala Lumpur International Airport at 00:42 MYT on Saturday, 8 March 2014.

In the first media statement by Malaysia Airlines at 7:30 am it was stated that contact with the aircraft had been lost:-

Sepang, 8 March 2014: Malaysia Airlines confirms that flight MH370 has lost contact with Subang Air Traffic Control at 2.40am, today (8 March 2014).

Source:

It would be more accurate to say that there was a progressive loss of contact, as shown by the list of events below:-

1. VHF Radio Communications Ceased
   

   At 1:19:30 MYT Captain Zaharie Shah communicated with Malaysian Air Traffic Control using a VHF radio, saying “Good night Malaysian Three Seven Zero”. This was the last recorded radio transmission from MH370. Malaysian Air Traffic Control had instructed MH370 to contact Vietnamese Air Traffic Control, but this did not happen either.

2. Radar Transponder on MH370 Stopped Responding
   

   Air Traffic Controllers monitor two types of radar. Primary radar broadcasts a strong radio signal and receives weak reflections from objects such as an aircraft. The received signal is interpreted but provides only basic information only. Secondary radar is more useful because when a lower-powered radar system on the ground transmits a radio signal a receiver on an aircraft, such as MH370, receives that signal and responds by transmitting information about the aircraft, including its' location, altitude, heading (direction) and more. The device which transmits in response to the radar signal is called a transponder.

   At 01:20:36 MYT the symbol representing MH370 disappeared from the radar display monitored by air traffic controllers at Kuala Lumpur. The same event was captured by both Thai and Vietnamese radar. For safety reasons the transponder should be operating at all times during flight. But on MH370 the transponder stopped.

3. ACARS Stopped Sending Messages
   

   ACARS is a low-technology messaging system that has been adapted to send data over a satellite communications link. One of the messages sent automatically is called a Position Report. For this report data on MH370 was collected every five minutes and a combined report was supposed to be sent every thirty minutes. Except it wasn't.

   The last position report was transmitted from MH370 over a satellite communications link at 01:07:29 MYT. The next report should have been transmitted automatically by MH370 at approximately 01:37 MYT. This report was never sent.

   Investigators concluded that the on-board ACARS equipment either failed, or was disabled or powered down at some time between 01:07:48 and around 02:25:00 (MYT).

4. Satellite Communication Link Failure
   

   At 02:03:23 MYT Malaysia Airlines sent a message to MH370, direct to the cockpit printer. This message requested the crew to contact the Ho Chi Minh Air Traffic Control immediately. If MH370 had continued on the Filed Flight Plan the aircraft would have been in Vietnamese air space but out of range for VHF radio to contact air traffic controllers in Malaysia. Although described as an ACARS message, transmission of this message involved a satellite communication link between the Inmarsat ground station and the aircraft MH370.

   However, an incoming downlink message at 02:03:24 MYT showed the message failed to reach the aircraft. The message was retransmitted (automatically) at least seven times. On each occasion, an automated downlink message by ACARS showed ‘failed’.

   Investigators concluded that the SATCOM Link was lost (by MH370) at some time between 01:07:48 and 02:03:41 (MYT).

Summary

At 01:19:30 when Captain Shah was responding to an air traffic controller all communication systems on MH370 were functional. Captain Shah was talking using a VHF radio. The transponder was working and the symbol representing the aircraft was visible on a radar screen. The most recent position report had been collated and sent, about 12 minutes earlier, by the ACARS messaging system over a satellite communications link.

But: the Captain did not contact Vietnamese air traffic control using VHF radio, either by choice or because of a technical issue or maybe he was prevented from doing so. If there is a problem onboard an aircraft the transponder code can be changed to indicate a hijack, for example, but instead the transponder seems to have been disabled or became non-functional for an unknown reason. And by the time Malaysia Airlines attempted to contact the Flight Crew the satellite communications system had also failed, or more likely been disabled.

An Anomaly

At 02:25:27 MYT the satellite data unit (SDU) on MH370 seems to have recovered from a power interruption and initiated a log-on sequence with the Inmarsat satellite communication system. This procedure is called a handshake.

However, although the link was subsequently available no communication to the aircraft was ever successful and there was no communication from any person or system on the aircraft.

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Malaysian Time (MYT) is Coordinated Universal Time (UTC) + 8 hours

Very High Frequency

Captain and Pilot in Command, MH370

A device that emits an identifying signal in response to an interrogating received signal from a communications satellite or ground station. (Source: ATSB)

Primary (or terminal area) radar relies on radio waves reflecting off metallic objects and is effective within a short range from the radar head, which is usually located at an airport. (Source: ATSB)

Secondary (or en route) radar returns are dependent on a transponder in the aircraft to reply to an interrogation from a radar ground station. (Source: ATSB)

Aircraft Communication and Reporting System

Filed Flight Plan – The flight plan as filed with an Air Traffic Services unit by the pilot or his designated representative, without any subsequent changes.

satellite communication from the aircraft to the ground earth station

Satellite Communications

Satellite Data Unit