Chronology/Satellite Communications Ground Station Logs

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Chronology: Satellite Communications Ground Station Logs

This article presents extracts from the Safety Investigation Report MH370/01/2018 which have been selected because the content is a chronology of events related to Malaysia Airlines flight MH370.

Each event in this chronology has been linked to a Timeline Event in the main Timeline articles on this site. This provides a cross-link or check on the well known events.


Table 1.9C - Chronology of Satellite Communications Ground Station Logs

Note: This Table is repeated in the article Satellite Ground Station Logs - Key Observations which also includes an Analysis of these events.



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No. Time (UTC) Key Observations - Satellite Ground Station Logs
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, suggesting that ADIRU (Air Data Inertial Reference Unit) navigation data was not available to the SDU at this time. No flight ID is sent to the GES at this time. This is the first SATCOM activity recorded at the GES since 0802:27, suggesting that the SATCOM was not powered for a period of several hours, whilst the aircraft was on ground. This is quite normal.
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. This suggests that the ADIRU derived navigation data has become available at this time.
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. This suggests that the IOR is now considered to be the best available satellite. This is probably because either the line of sight to the IOR satellite is now clearer than that to the POR satellite, or the antenna gain in the direction of the IOR satellite has become higher than the antenna gain in the direction of the POR satellite.
5. 1642:04 After take-off, the IFE SMS e-mail application sends a normal beginning-of-flight message.
  1. The message contained the correct AES ID, Flight ID "MAS370", origin airport "WMKK", and destination airport "ZBAA".
  2. 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 DATA-2 ACARS Message received at the GES. No further SATCOM Data-2 ACARS messages or acknowledgements were received at the GES for the remainder of the flight. This is abnormal and suggests that the on-board ACARS equipment either failed, or was disabled or powered down at some time between 1707:48 and around 1825:00.
7. 1803:41 GES initiates a DATA-2 ACARS transmission (uplink), but receives no acknowledgement from the SATCOM.
  1. Therefore, the SATCOM Link was lost at sometime between 1707:48 and 1803:41.
  2. There is no evidence of a cockpit-initiated manual Log-Off of the SATCOM.
  3. Note that even if the on-board ACARs equipment was failed, disabled or powered down at this time, it would not prevent the SATCOM from acknowledging the ACARS-related P-Channel transmissions from the GES.
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.
  1. This is the first ‘handshake’.
  2. This marks the end of the link lost period that began at sometime between 1707:48 and 1803:41.
  3. This log-on request suggests that whatever caused the SATCOM link loss to occur between 1707:48 and 1803:41 had been reversed.
10. 1825:34 SATCOM Log-On, successfully completed.
  1. 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).
  2. No Flight ID was sent to the GES during the Log-On. This implies that the SDU stopped receiving a valid Flight ID from the AIMS at sometime between 1642:04 and 1825:00.
  3. The possible reasons for the link loss and the subsequent Log-On that took place at 1825:00 have been investigated and are detailed in Table 2.5A. There are many quite complicated scenarios that could have caused the 1825:00 Log-On. However, the most likely reason is a power interrupt to the SATCOM avionics, of a duration greater than 22 minutes (the time between events 7 and 9) and less than 78 minutes (the time between events 6 and 9).
  4. The GES recorded an abnormal BFO for the SATCOM Log-On Acknowledge transmissions (Sections 1.9.5 para. 5 and 2.5.3).
    • 1825:00 Log-On Acknowledge - Most likely due to the power-on drift of the Oven Controlled Crystal Oscillator (OCXO), thus endorsing the belief that the 1825:00 Log On was preceded by a lengthy power interrupt.

An OCXO provides a stable reference frequency for the SDU Radio Frequency (RF) transmit and receive circuits and also for SDU modem timing. Within the OCXO, a regulated oven keeps the crystal at an almost constant temperature if the ambient temperature in the crown area is between the ranges -55oC up to above +70oC. The oven also contains extra electrical regulation and isolation to ensure frequency accuracy and stability. The OCXO includes an oven ready flag, which triggers the Log-On initiation when the OCXO reaches its operating temperature. Extensive laboratory testing has revealed that during warm up, the OCXO frequency may vary non-linearly with time, but then settles with almost negligible variation. At power-on, the OCXO can exhibit either a rising or falling frequency gradient, before decaying over time to its normal steady state value. The testing has indicated that reasonable stability (within 2Hz/minute) is typically reached by around five minutes after an initial peak or overshoot. The testing has also shown that there can still be a significant frequency offset at the time that the oven ready flag initiates the Log-On process, so the Log-On request, Log-On Acknowledge and subsequent data bursts can all exhibit significant frequency offsets.

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 (Malaysia)
  1. Q10 Airline Operational Communications (AOC) Priority Level
  2. The Perth GES logs indicate that a good link is likely to have existed at this time.
  3. 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.
  4. 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
  1. 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.
  2. 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
  1. This is the third ‘handshake’.
  2. 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
  1. This is the fourth ‘handshake’.
  2. 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
  1. This is the fifth ‘handshake’.
  2. 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 (Malaysia)
  1. Q10 AOC Priority Level.
  2. The Perth GES logs indicate that a good link is likely to have existed at this time.
  3. 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.
  4. 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
  1. This is the sixth ‘handshake’.
  2. 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’.
  1. For there to have been a Log-On at this time, there must have been a prior loss of the SATCOM link. This link loss must have occurred at some time after 0010:58, when the SATCOM responded to a Log-On interrogation.
  2. This Log-On request suggests that whatever caused the SATCOM link loss to occur had been reversed.
23. 0019:37 SATCOM Log-On, successfully completed
  1. The SATCOM link becomes available (for voice and data – Class 3) once more and normal SATCOM operation resumes.
  2. No Flight ID was sent to the GES during the Log-On. This infers that the SDU was still not receiving the Flight ID from AIMS.
  3. The possible reasons for the link loss and the subsequent Log On that took place at 0019:00 have been investigated and are detailed in Section 2.5.2. There are many quite complicated scenarios that could have caused the 0019:00 Log-On with no Flight ID. However, the most likely reason is a power interrupt to the SATCOM avionics, of a duration less than 8 minutes.
  4. The GES recorded an abnormal frequency offset for the SATCOM Log-On Request and Acknowledge transmissions (see Sections 1.9.5 para. 5) and 2.5.3). The abnormal BFOs for the 0019 Log-On Request and Log-On Acknowledge are more likely due to a combination of uncompensated vertical velocity (descent) and OCXO warm up drift.
  5. The IFE did not subsequently establish the two Data-3 X.25 connections over the SATCOM, which it normally does if it is functional. It can be inferred that the IFE was either not operating at this time (powered off, not being powered whilst the SATCOM was being powered by the APU, failed, or still resetting after a power cycle), or the SATCOM and/or the IFE became inoperative before the IFE was able to establish the Data-3 connection


Note: 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
  1. The SATCOM Link was lost at sometime between 0019:37 and 0115:56.
  2. There is no evidence of a cockpit-initiated manual Log-Off of the SATCOM.
  3. The loss of SATCOM link was due to one of the following:
    1. The SATCOM stopped receiving the P-Channel transmission from the satellite
    2. SATCOM input power (115VAC 400Hz) was removed
    3. The SATCOM experienced a BITE failure.
25. 0116:06 Log-On Interrogation by the Perth GES, with no response from the SATCOM.
26. 0116:15 Log-On Interrogation by the Perth GES, with no response from the SATCOM.

Table 1.9C - Chronology of Satellite Communications Ground Station Logs


Source: Malaysian ICAO Annex 13 Safety Investigation Team for MH370, 02 July 2018, Safety Investigation Report MH370/01/2018