MH370 Timeline - Turn South
- 1 Flight MH370 Timeline - the Turn South
- 2 Turn South
- 2.1 Background
- 2.2 1. Last Primary Radar Observation at 1822:12 UTC (0222:12 MYT)
- 2.3 2. SATCOM Log-on Request at 1825:27 UTC (0225:27 MYT)
- 2.4 3. Other Satellite Communications
- 2.5 Table 1.9B - SATCOM ‘Handshakes’
- 2.6 4. Telephone Call at 1839:52 MYT
- 2.7 5. A Possible Flight Path
- 2.8 6. Summary: The Turn South
- 2.9 Notes and References
Flight MH370 Timeline - the Turn South
Details of the final turn South made by MH370 are not known. This Section provides an overview of what is known, or inferred by other data.
At the time of the last primary radar observation of MH370 at 0222:12 MYT the aircraft was located north-east of the northern tip of Sumatra and was heading north-west towards the Andaman Sea.
At 0341:00 MYT the Inmarsat ground station initiated a Log-On Interrogation, with a response from the SATCOM on MH370. Analysis of the metadata associated with this transmission indicated that the aircraft was, at that time, travelling south.
So, at some time between 0222:12 MYT and 0341:00 MYT, MH370 changed direction and turned south.
The sections below provide more detail in support of this statement, and also some refinements which narrow the time range during which the turn was made.
Throughout this website Malaysian Time (MYT) has been used as much as possible. On this page, however, the extracts which have been quoted, and the graphics which have been referenced, use Universal Coordinated Time (UTC). This is primarily because the satellite communications and radar observations have been referenced in UTC.
On the graphics, and captions, it can be assumed that times are UTC.
MYT is UTC plus 8 hours.
1. Last Primary Radar Observation at 1822:12 UTC (0222:12 MYT)
The last Military primary radar observation of MH370 is described in the Safety Investigation Report MH370/01/2018 as follows:-
At 1803:09 UTC [0203:09 MYT] the “blip” disappeared, only to reappear at 1815:25 UTC [0215:25 MYT] until 1822:12 UTC [0222:12 MYT], about 195 nm from Butterworth, on a heading of 285°, speed of 516 kt and at an altitude of 29,500 ft.
The radar track of MH370 is shown in Figure 2 opposite.
- The civilian Air Traffic Control radar track (secondary radar) is shown as the pale line from Kuala Lumpur to the last secondary radar observation at 1722 UTC (0122 MYT).
- The Military primary radar track is shown as a yellow line from the turnback near waypoint IGARI, across Malaysia and north-west along the Malacca Strait.
The exact latitude and longitude of MH370 at 0222:12 MYT is not provided, but from the graphic it can be seen that MH370 is located north-east of the tip of Sumatra and heading north-west towards the Andaman Sea.
Figure 2: MH370 flight path derived from primary and secondary radar data
Source: MH370 - Definition of Underwater Search Areas, Australian Transport Safety Bureau, 2014.
2. SATCOM Log-on Request at 1825:27 UTC (0225:27 MYT)
At 0225:27 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. The satellite data link was lost some time between 1707:48 and 1803:41 UTC, possibly due to a loss of electrical power. The reasons for these events is discussed in the Safety Investigation Report MH370/01/2018 and the extracts linked from each event in the Timeline.
Investigators have called this log-on event the first ‘handshake’ - because it was a successful communication between the aircraft and the ground station via the satellite.
The other benefit of this communication is the metadata associated with this transmission - the Burst Timing Offset (BTO) provides an indication of the distance of the aircraft from the satellite at that time. This is shown graphically (with other 'handshakes') as a series of concentric circles, or rings, in Figure 18 below. Since only part of the ring is technically feasible, the valid section is called an 'arc'.
In the diagram opposite, the position of MH370 is shown on this first, 1825 UTC arc.
It seems unlikely that the heading has changed significantly in the short period since the last primary radar observation.
Fig. 4.3 18:02 prediction to 18:25, shown in yellow. The Malaysian military radar track is shown in white, on the right. The near-vertical white line on the left corresponds to the 18:25 BTO arc.
Source: Bayesian Methods in the Search for MH370
3. Other Satellite Communications
After the successful log-on which commenced at 0225:27 MYT there were a series of automated communications, and two unsuccessful telephone calls from Malaysia Airlines.
Because the SATCOM was logged-on, the ground station periodically communicated with it to check that it was still logged on. These automated transmissions should occur approximately every hour.
However, the two telephone calls using the satellite system had the effect of resetting the timer at the ground station, so the 'handshakes' initiated by the ground station were not one hour apart.
The Table below shows the sequence of handshakes and phone calls. The metadata associated with the transmissions for each 'handshake' enabled Investigators to calculate the distance of the aircraft from the satellite at the time of each event. This is shown as a series of concentric rings in the diagram below right. The Time on each ring is UTC.
Table 1.9B - SATCOM ‘Handshakes’
|1.||Aircraft departed KLIA||1642:04||0042:04|
|2.||Last ACARS transmission||1707:48||0107:48|
|3.||1st handshake - log-on initiated by the aircraft||1825:27||0225:27|
|4.||Unanswered ground-to-air telephone call||1839:52||0239:52|
|5.||2nd handshake initiated by ground station||1941:00||0341:00|
|6.||3rd handshake initiated by ground station||2041:02||0441:02|
|7.||4th handshake initiated by ground station||2141:24||0541:24|
|8.||5th handshake initiated by ground station||2241:19||0641:19|
|9.||Unanswered ground-to-air telephone call||2313:58||0713:58|
|10.||6th handshake initiated by ground station||0010:58*||0810:58|
|11.||7th handshake - log-on initiated by the aircraft||0019:29*||0819:29|
|12.||Aircraft did not respond to ‘handshake’ from Satellite Earth Ground Station||0115:56*||0915:56|
|*08 March 2014|
Table 1.9B - SATCOM ‘Handshakes’
Source: Malaysian ICAO Annex 13 Safety Investigation Team for MH370, 02 July 2018, Safety Investigation Report MH370/01/2018
Note: Table 1.9B, when published, showed times rounded to the nearest minute. The above version has been updated to include seconds, so that each time can be linked to the correct event in the Timeline. No other data has been changed. The two versions can be seen together here.
Figure 18: BTO ring solutions for 9M-MRO
Source: MH370 - Definition of Underwater Search Areas, Australian Transport Safety Bureau, 2014.
Note: Each yellow arrow points to a 'ring', using the time as a label. The arrow does not indicate the position of MH370 at that time.
4. Telephone Call at 1839:52 MYT
Malaysia Airlines made two attempts to contact MH370 by telephone over the satellite communications system. The first was at 1839:52 UTC (0239:52 MYT). Analysis of the metadata related to this transmission - the Burst Frequency Offset (BFO) indicates that MH370 was heading south at that time. For interest, here is an extract from the paper Bayesian Methods in the Search for MH370 which 'explains' the analysis:-
The first call occurred from 18:39:53 to 18:40:56 and is important because the measured BFO is significantly different from the BFO on the R1200 measurement preceding it at 18:28:15. The R1200 BFO value is consistent with the speed and direction of the aircraft while under radar coverage whereas the later C-channel BFO value is not. Assuming that the change in BFO implies a turn, the difference between the BFO predicted by using a MATLAB model of the SDU software1 and the measured BFO on the C-channel was analysed as a function of post-turn direction and for a range of aircraft speeds and turn times between 18:28:15 and 18:39:53. Figure 5.6 shows the residual error and it clearly demonstrates that only Southerly track angles are consistent with the C-channel measurements. The model predicted BFO values of Northerly paths are more than 10 standard deviations away from the measured BFO.
After the successful log-on by the satellite data unit of MH370, the In-Flight Entertainment System set up a connection over the satellite link (for built-in test equipment) at 1828:05 UTC. At that time, MH370 was still north of Sumatra and on much the same heading as the last primary radar observation. When this metadata (the Burst Frequency Offset measurement) was compared with the BFO values for the phone call at 1839:53 UTC they were not the same. So the aircraft must have changed direction. By considering both a northerly change and a southerly change the mathematicians found that the direction with the highest probability, was to the south.
5. A Possible Flight Path
There are many variables to consider when defining the time when MH370 turned south. Investigators have worked hard to refine their mathematical models so that they can predict more accurately where the flight ended.
Obviously, we do not know the exact time that a turn commenced. There have been many attempts to reconstruct a flight path using an early turn; a late turn; or some time in-between. Each solution must still place the aircraft on one of the seven arcs at the time of the relevant satellite communication.
An aircraft can also make different types of turn - gentle and level is normal for passenger flights; or steeply banked; maybe with some acceleration through the turn; or a change of altitude. There are many possibilities, including whether the turn was manually controlled or executed by the autopilot.
One of the valid flight paths is shown in the diagram opposite. This one was created by engineers from Inmarsat who did the original calculations with the values of Burst Timing Offset and Burst Frequency Offset. Without this innovative analysis of the metadata we would have absolutely no idea where MH370 went after flying beyond Malaysia's military radar coverage.
The flight path shown here is 'indicative' - it represents a likely end-of-flight path in a southerly direction with its' heading changing from 186° to 180° by the end of the flight.
Note: Although MH370 was close to the northern tip of Sumatra, it likely crossed, or was close to, Indonesian airspace. But there is no radar data from Indonesia.
Figure 17. Example Flight Path.
Source: The Search for MH370, Chris Ashton, Alan Shuster Bruce, Gary Colledge and Mark Dickinson (Inmarsat), as published in The Journal of Navigation (2015)
6. Summary: The Turn South
The satellite communications company Inmarsat developed an innovative method to use the metadata from satellite communications with MH370 to determine its' approximate distance from the satellite during events called 'handshakes' which were two-way communications between MH370 and a ground station in Perth, Western Australia. The metadata involved two measurements - the Burst Timing Offset and the Burst Frequency Offset. The calculations performed by Inmarsat were peer reviewed and subsequently refined by many experts, including mathematicians at the Defence Science and Technology Group in Australia. Transmissions prior to a turn when MH370 was still heading north west along the Malacca Strait, and transmissions after a turn when MH370 was heading south, have narrowed the time that a turn was made to between 1828:05 UTC (0228:05 MYT) and 1839:52 UTC (0239:52 MYT).
Focussing on only one type of metadata - the Burst Timing Offset - yields two valid directions for MH370 to travel. These were called the 'Northern Corridor' and the 'Southern Corridor' and are defined by seven arcs representing the distance between MH370 and the satellite at the time of each of seven 'handshakes'. None of the countries on the Northern Corridor had any radar record of MH370 flying through their airspace, and no wreckage has been found in those areas.
The second type of metadata - the Burst Frequency Offset - provided investigators with evidence that MH370 travelled south. The measurements were compared with and validated by data from other flights; and the conclusion that MH370 not only turned south but also ended the flight in the south Indian Ocean is consistent with all other evidence available to date, for example debris recovered which would have drifted from the crash site.
The unsuccessful attempts to locate the aircraft does not invalidate the above statements and conclusion. It is merely a confirmation of how large the Indian Ocean is, and the complexity of the task. That we know anything at all about the flight after MH370 left Malaysian airspace and flew beyond Malaysia's military radar capability is a tribute to all those scientists, engineers and mathematicians who have devoted so much energy to solving such a complex enigma.
Notes and References
- MH370 - Definition of Underwater Search Areas, Australian Transport Safety Bureau, 2014.
- Bayesian Methods in the Search for MH370, Samuel Davey, Neil Gordon, Ian Holland, Mark Rutten and Jason Williams, © Commonwealth of Australia 2016. ISBN 978-981-10-0379-0 (eBook)
The authors collaborated on this project for the Defence Science and Technology (DST) Group (Australia) to support the Australian Transport Safety Bureau underwater search for MH370.
- The Search for MH370, Chris Ashton, Alan Shuster Bruce, Gary Colledge and Mark Dickinson (Inmarsat), as published in The Journal of Navigation (2015)
This Timeline has been created by deconstructing official documents and linking these extracts in a way which simulates a chronological sequence and facilitates access to further detail and explanatory notes for time-related events in the narrative of Malaysia Airlines flight MH370.