Factual Information 2015:1.9 Communications/1.9.5 Satcom
This page contains an extract from MH370/01/15 Factual Information which accompanied the (first) Interim Statement released by The Malaysian ICAO Annex 13 Safety Investigation Team for MH370 on 8th March 2015.
1.9.5 Satellite Communications (SATCOM)
1.9.5.1 SATCOM System Description
SATCOM is an acronym of, and generic term for, satellite communications. SATCOM operates by using satellites to relay radio signals between the sender and receiver. It can cover far more distance and wider areas than other radios. SATCOM can be used to transmit words, pictures and other forms of information.
The aircraft, 9M-MRO, was equipped with a SATCOM terminal that used the Inmarsat Classic Aero system. The Inmarsat system utilises a constellation of satellites to provide nearly global coverage, the exception being polar areas. The aircraft SATCOM system, also referred to as an Airborne Earth Station (AES) operates on L Band, transmits at 1.6 GHz and receives at 1.5 GHz. For this aircraft, the SATCOM system provided a total of five voice channels and one data channel. The satellite link provides the following functions:
The Earth or Ground Station uses C Band, transmits at 6 GHz and receives at 4GHz.
Inmarsat uses a network of Ground Earth Stations (GES) to communicate with the satellites and connect the SATCOM signal to other terrestrial data networks such a telephone systems, internet, etc.
When the SATCOM AES is first powered on, it sends a log-on request to the GES to initiate service. There are a number of channels available for messages to be sent between the Satellite and Earth Station. One of the channels is called the ‘common access channel’, which aircraft will constantly listen to when able to do so. If the GES has not heard from an aircraft for an hour after the last communication, it automatically transmits a ‘log on/log off’ (“ping”) message on the common access frequency using the aircraft’s unique identifier. If the aircraft receives its ‘unique identifier’, it returns a short message that it is still logged onto the network. Both the initial log-on request and the hourly ping have been termed as a ‘handshake'.
The SATCOM AES consists of the following equipment: Radio frequency unit (RFU), Radio frequency attenuator (RF ATTN), Radio frequency splitter (RFS), Class C high power amplifier (HPA), Class A high power amplifier (HPA), High power relay (HPR), three low noise amplifier/diplexers (LNA/DIPs), Low gain antenna (LGA), two beam steering units (BSUs), two high gain antennas (HGAs), Radio frequency combiner (RFC) and Satellite data unit (SDU).
The SATCOM avionics are located on the E11 rack, which is in the crown area aft of doors 3 left/right. The High Gain antennas are mounted above door 3 left and door 3 right. The Low Gain antenna is mounted on the fuselage centreline. The SATCOM Circuit Breakers (CB) are located in the Main Equipment Center (MEC).
The Satellite Data Unit (SDU) receives 115v ac from the Left Main bus.
The diagram in Figure 1.9L below shows the complete set of SATCOM units, including avionics, High Gain Antenna Subsystem and Low Gain Antenna Subsystem. It also shows interfaces to the aircraft cockpit and cabin systems and functions. The following notes are intended to be read in conjunction with Figure 1.9L:
- CDU (3) are the three Control Display Units, otherwise known as Multi-function Control Display Units (MCDUs).
- CPMU is Cabin Passenger Management Unit, which provides an interface between the Panasonic IFE and the SDU, for any Data-3 SMS/e-mail messages.
- AMU is the Audio Management Unit, which feeds cockpit audio to and from the SDU.
- CTU is the Cabin Telecommunications Unit, which provides an interface between the in-seat handsets and the SDU, for cabin telephony calls, were that functions available. In the case of 9M-MRO, the in-seat phones can only be used for seat-to-seat calling.
- AIMS Cabinet is one of two Airplane Information Management System cabinets, which route numerous information to and from the SDU, including ACARS data, Navigational data, AES ID and Flight ID.
- SATCOM Maintenance Switch is not relevant to this document, as no maintenance activity is possible in flight.
The photo in Figure 1.9M below shows the Honeywell/Racal (Honeywell/Thales) MCS-6000 SATCOM Units – RFU (left), SDU (centre) and HPA (right)
1.9.5.2 SATCOM Ground Station Logs of the Event – Introduction
Throughout the flight of MH370, the aircraft communicated through the Inmarsat Indian Ocean Region (IOR) I-3 Satellite and the GES in Perth, Australia.
Figure 1.9N shows the Inmarsat I-3 IOR Satellite Coverage Map. The blue lines represent the elevation angle to the IOR satellite for a SATCOM unit on the ground or in the air. Due to the satellite inclination, the elevation angles are approximate.
MH370 departed KLIA at 1642 UTC (0042 MYT, 8 March 2014). At 1707 UTC, the SATCOM system was used to send a standard ACARS report, normally sent every 30 minutes. This message indicated there was sufficient fuel for MH370 to remain airborne until approximately 0012 UTC [0812 MYT]. The ACARS reports expected at 1737 UTC and 1807 UTC were not received. The next SATCOM communication was a log-on request from the aircraft at 1825 UTC. From that point until 0010 UTC, SATCOM transmissions indicate that the link was available, although not used for any voice, ACARS or other data services. At 0019 UTC, the AES initiated another log-on request. This was the last SATCOM transmission received from the AES.
Apart from a short period around 1825 UTC [0225 MYT, 8 March 2014], the SATCOM link was available for the major part of the flight. Data from the last seven ‘handshakes’ were used to help establish the most probable location of the aircraft. Initially only the first six of these ‘handshakes’ were considered to be complete. The seventh and last ‘handshake’ that was automatically initiated by the aircraft, was originally assessed as a partial ‘handshake’. Subsequent analysis confirmed the 7th handshake could be used to help determine the most probable flight path. Two unanswered ground-to-air telephone calls had the effect of resetting the activity log and hence increased the period between the ground initiated ‘handshakes’. The significant times used to identify the most probable final location of the aircraft are tabulated in Table 1.9B below. Details of the event’s SATCOM ground station logs are provided in paragraphs 1.9.5.3 and 1.9.5.4 below.
| SATCOM TRANSMISSIONS
|
TIME | ||
|---|---|---|---|
| UTC | MYT* | ||
| 1 | Aircraft departed KLIA | 1642 | 0042 |
| 2 | Last ACARS transmission | 1707 | 0107 |
| 3 | 1st handshake – log-on initiated by the aircraft | 1825 | 0225 |
| 4 | Unanswered ground-to-air telephone call | 1839 | 0239 |
| 5 | 2nd handshake initiated by ground station | 1941 | 0341 |
| 6 | 3rd handshake initiated by ground station | 2041 | 0441 |
| 7 | 4th handshake initiated by ground station | 2141 | 0541 |
| 8 | 5th handshake initiated by ground station | 2241 | 0641 |
| 9 | Unanswered ground-to-air telephone call | 2313 | 0713 |
| 10 | 6th handshake initiated by ground station | 0010* | 0810 |
| 11 | 7th handshake – log-on initiated by the aircraft | 0019* | 0819 |
| 12 | Aircraft did not respond to ‘handshake’ from Satellite Earth Ground Station | 0115* | 0915 |
| * 08 March 2014 | |||
Table 1.9B SATCOM ‘Handshakes’
1.9.5.3 SATCOM Ground Station Logs of the Event - Summary
The SATCOM utilised the Inmarsat Indian Ocean Region (IOR) I-3 satellite and the associated Perth Ground Earth Station (GES) throughout the flight. Inmarsat has confirmed that during the flight, no SATCOM signalling or traffic was routed via any other satellites (including MTSAT) to any other GESs (including MTSAT7 GESs). The SATCOM provided the Satellite link for the following functions:
- Cockpit Voice - Call control via the Multi-function Control and Display Units (MCDUs) and audio via the cockpit Audio Management Unit (AMU) and associated headsets
- Cockpit Packet Data (Data-2) - Interface via the ACARS Management Unit (MU)
- Cabin Packet Data (Data-3) - Interface via the Panasonic System 3000i IFE equipment:
The GES logs contain the following key information for each transmission to and from the aircraft:
- Time tag, Satellite and GES (Note: the timestamp accuracy does vary between the different logs, but should always be <1 second, and usually to a few milliseconds)
- Channel Type, Channel Number (frequency), Received Carrier/Noise Density Ratio (C/No), channel Bit-Error-Rate (BER), Burst Frequency Offset (BFO) and Burst Timing Offset (BTO, or round trip delay).
- All payload data (excluding voice frames) contained within the transmission – these are known as the Signal Unit contents.
The events are summarised below. All times are in UTC. In the summary below, times are truncated to the nearest minute (the format is Hours:Minutes) and in Section 1.9.5.4, times are truncated to the nearest second (the format is Hours Minutes:Seconds).
1. Prior to take-off, the SATCOM Logged On (normally) a number of times, the last time being at 16:00, when it sent a valid Flight ID to the GES. The SATCOM link was available for both voice and data (known as Log-On Class 3).
2. After take-off, the IFE SMS e-mail application sent a normal beginning-of-flight message at 16:42 (containing the correct Airborne Earth Station [AES ID], Flight ID "MAS370", origin airport "WMKK", and destination airport "ZBAA"), indicating that the IFE was receiving the valid Flight ID, origin airport and destination airport from AIMS and the ICAO (AES) ID from the Satellite Data Unit (SDU) at this time.
3. The SATCOM link was available for most of the flight, excluding periods leading up to 18:25 UTC, 07 March and 00:19 UTC, 08 March 2014.
4. When the SATCOM link was re-established at the above times, no Flight ID was present.
5. During each of the two in-flight Log-Ons at 18:25 UTC and 00:19 UTC, the GES recorded abnormal frequency offsets for the burst transmissions from the SATCOM.
6. There is no indication of the SATCOM link being manually Logged Off from the cockpit (via an MCDU). Such activity would have been captured in the GES logs, but it was not.
7. No Data - 2 ACARS traffic was observed after 17:07 UTC, 07 March 2014.
8. The IFE equipment set up two ground connections over SATCOM (for the SMS e-mail application and Built-In Test Equipment (BITE) application) after the SATCOM re-established the link at 18:25 UTC, 07 March 2014 (normal), but not after the SATCOM re-established the link at 00:19 UTC, 08 March (abnormal). At no time during the flight was any user data sent over the link by means of the SMS/e-Mail application.
9. Two Ground-to-Air Telephony Calls were placed to the cockpit from the MAS Operations Centre at Airline Operational Communications (AOC) Q10 priority level at 18:39 UTC and at 23:13 UTC, 07 March. Neither of the calls was answered.
10. The SATCOM responded normally to a series of roughly hourly Log-On Interrogations from the Perth GES, up to and including a Log-On Interrogation at 00:10 UTC, 08 March 2014. The two unanswered ground to air calls at 18:39 UTC and 23:13 UTC reset the Perth GES inactivity timer and hence the Log-On Interrogations were not always hourly.
11. The last transmission received from the SATCOM occurred at 00:19 UTC, 08 March 2014 and the SATCOM failed to respond to a series of three Log-On interrogations starting at 01:15 UTC, 08 March.
7 MTSAT – A series of Japanese weather and aviation satellites and GESs. MTSAT-1R and MTSAT-2 satellites are interoperable with Inmarsat satellites.
1.9.5.4 SATCOM Ground Station Logs - Key Observations in Chronological Order
1. 1250:19 - Prior to take-off, the SATCOM initiates a normal Log-On as Class 1 (data only capable) via the Pacific Ocean Region (POR) I-3 satellite, using the Low Gain Antenna (LGA) subsystem. No flight ID is sent to the GES at this time. This is the first SATCOM activity recorded at the GES since 0802:27.
2. 1555:57 - The SATCOM initiates a normal Log On Renewal as Class 1 (data only capable) via the POR I-3 satellite, using the LGA subsystem, this time with a valid Flight ID.
3. 1557:49 - The SATCOM initiates a normal Log-On as Class 3 (voice and data capable) via the POR I-3 satellite, using the High Gain Antenna (HGA) subsystem, with a valid Flight ID.
4. 1559:57 - The SATCOM initiates a Log-On handover as Class 3 (voice and data capable) to the IOR I-3 satellite, using the HGA subsystem, with a valid Flight ID.
5. 1642:04 - After take-off, the IFE SMS e-mail application sends a normal beginning-of-flight message.
a. The message contained the correct AES ID, Flight ID "MAS370", origin airport "WMKK", and destination airport "ZBAA".
b. This indicates that the IFE was receiving the Flight ID, origin airport and destination airport from AIMS and the ICAO (AES) ID from the SDU at this time.
6. 1707:48 - Last Acknowledged DATA-2 ACARS Message. No further SATCOM Data-2 ACARS messages or acknowledgements were received at the GES for the remainder of the flight.
7. 1803:41 - GES initiates a DATA-2 ACARS transmission (uplink), but receives no acknowledgement from the SATCOM.
a. Therefore, the SATCOM Link was lost at sometime between 1707:48 and 1803:41.
b. There is no evidence of a cockpit-initiated manual Log-Off of the SATCOM.
8. 1805:11 - GES initiates a DATA-2 ACARS transmission, but receives no acknowledgement from the SATCOM, indicating that there is still no SATCOM link at this time.
9. 1825:27 - SATCOM Log-On, initiated from the aircraft terminal.
a. This is the first ‘handshake’.
b. This marks the end of the link lost period that began at sometime between 1707:48 and 1803:41.
10. 1825:34 – SATCOM Log-On, successfully completed.
a. The SATCOM link becomes available (for both voice and data – Class 3) once more and normal SATCOM operation resumes (except that there is no Data-2 ACARS traffic which is normally transmitted at least once every 30 minutes).
b. No Flight ID was sent to the GES during the Log-On.
c. The GES recorded abnormal BFOs for the SATCOM Log-On Request and Log-On Acknowledge transmissions.
11. 1827:03 – The IFE sets up a Data-3 ground connection (X.25 circuit) over SATCOM for an SMS/e-mail application after the SATCOM link is re-established.
12. 1828:05 – The IFE sets up a Data-3 ground connection (X.25 circuit) over SATCOM for a BITE application after the SATCOM link is re-established.
13. 1839:52 – Ground to Air Telephony Call Placed from a number with country code 60
a. Q10 Airline Operational Communications (AOC) Priority Level
b. This call would have been routed to the cockpit and should have resulted in a chime and an incoming visual annunciation on the Audio Control Panels (ACPs), and, if the appropriate SATCOM page was selected, then also on one or more MCDU.
c. The GES logs show zero duration, indicating that the call went unanswered. Note that there are two methods for the answering of an incoming call: Either by pressing the relevant Line Select Key on an MCDU, or by keying a microphone.
14. 1840:56 – The GES logs show that the unanswered Ground to Air telephony call was cleared by the calling party.
15. 1941:00 – Log-On Interrogation by the Perth GES, with a response from the SATCOM
a. This is the second ‘handshake’, whereby the GES inactivity timer has expired and the GES has sent a message to interrogate the status of the SATCOM.
b. The SATCOM responded normally and the SATCOM link was therefore available at this time.
16. 2041:02 – Log-On Interrogation by the Perth GES, with a response from the SATCOM
a. This is the third ‘handshake’.
b. The SATCOM responded normally and the SATCOM link was therefore available at this time.
17. 2141:24 – Log-On Interrogation by the Perth GES, with a response from the SATCOM
a. This is the fourth ‘handshake’.
b. The SATCOM responded normally and the SATCOM link was therefore available at this time.
18. 2241:19 – Log-On Interrogation by the Perth GES, with a response from the SATCOM
a. This is the fifth ‘handshake’.
b. The SATCOM responded normally and the SATCOM link was therefore available at this time.
19. 2313:58 - Ground to Air Telephony Call Placed from a number with country code 60
a. Q10 AOC Priority Level.
b. This call would have been routed to the cockpit and should have resulted in a chime and an incoming visual annunciation on the Audio Control Panels, and, if the appropriate SATCOM page was selected, then also on one or more MCDU.
c. The GES logs show zero duration, indicating that the call went unanswered. Note that there are two methods for the answering of an incoming call: Either by pressing the relevant Line Select Key on an MCDU, or by keying a microphone.
20. 2315:02 - The GES logs show that the unanswered Ground to Air telephony call was cleared by the calling party.
21. 0010:58 - Log-On Interrogation by the Perth GES, with a response from the SATCOM
a. This is the sixth ‘handshake’.
b. The SATCOM responded normally and the SATCOM link was therefore available at this time.
22. 0019:29 - SATCOM Log-On, initiated from the aircraft terminal. This is the seventh ‘handshake’.
23. 0019:37 - SATCOM Log-On, successfully completed
a. The SATCOM link becomes available (for voice and data – Class 3) once more and normal SATCOM operation resumes.
b. No Flight ID was sent to the GES during the Log-On.
c. The GES recorded an abnormal frequency offset for the SATCOM Log-On Request and Acknowledge transmissions.
d. The IFE did not subsequently establish the two Data-3 X.25 connections over the SATCOM.
e. Note that this is the last transmission received from the aircraft terminal.
24. 0115:56 - Log-On Interrogation by the Perth GES, with no response from the SATCOM
a. The SATCOM Link was lost at sometime between 0019:37 and 0115:56.
b. There is no evidence of a cockpit-initiated manual Log-Off of the SATCOM.
25. 01:16:06 – Log-On Interrogation by the Perth GES, with no response from the SATCOM
26. 01:16:15 – Log-On Interrogation by the Perth GES, with no response from the SATCOM
Source: Malaysian ICAO Annex 13 Safety Investigation Team for MH370, 8 March 2015, Factual Information MH370/01/15
The Factual Information was updated in 2018 by the Safety Investigation Report MH370/01/2018 which added new content but did not include all of the previous data.