Flight MH370/2014-03-08/02-25-34 MYT

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Event Metadata

Flight ID	MH370
Event Type	air
Date and Time MYT	8 March 2014 02:25:34 MYT
Date and Time UTC	7 March 2014 18:25:34 UTC
Flight Phase	Phase 5
Data Source	Safety Investigation Report (2018) 1.9.4 / Table 1.9C (No. 10)
Date and Time ISO 8601	2014-03-07T18:25:34Z
ISO 8601 Description	Flight MH370 Event at 2014-03-07T18:25:34Z

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Event Summary

 02:25:34 MYT Saturday 8 March 2014

Chronology

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).

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.

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).

Event Details

1. Safety Investigation Report MH370/01/2018 Satellite Ground Station Logs - Key Observations

   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.

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Notes

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The short summary below is transcluded into a relevant Chronology page.

8 March 2014   02:25:34 MYT

SATCOM Log-On successfully completed; SATCOM link re-established for voice and Data Class 3. Abnormal Burst Frequency Offset (BFO) recorded, consistent with power interruption of the OCXO. No Flight ID transmitted during Log-On, indicating SDU had stopped receiving valid Flight ID from AIMS.

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Flight Identifier, for example MH370

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

Coordinated Universal Time

The Safety Investigation Report MH370/01/2018 was released by the Malaysian ICAO Annex 13 Safety Investigation Team for MH370 in July 2018. More Info

Satellite Communications

Aircraft Communication and Reporting System

Ground earth station. A satellite ground station sends or receives data from orbiting satellites. (Source: ATSB)

Satellite Data Unit

Airplane Information Management System

Burst Frequency Offset. BFO is a measure of the difference between the expected frequency of a satellite transmission and the frequency received at the ground station. See Burst Frequency Offset

Oven Controlled Crystal Oscillator