Safety Investigation Report 2018:1 Factual Information/1.9/1.9.5 Satcom/5
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SAFETY INVESTIGATION REPORT MH370 (9M-MRO)
1.9.5 Satellite Communications
5) Frequencies of Log-On Bursts
During each of the two in-flight Log-Ons that occurred at 1825 and 0019, the GES recorded abnormal frequency offsets for the SATCOM transmissions. This is in contrast with the ‘normal’ Log-On behaviour.
Table 1.9D (below) shows the frequencies of these Log-On bursts, as measured at the GES, plus differences from assumed reference frequencies (closest stable values in time, where the aircraft is assumed to be in level flight). The table also shows the very high delta frequencies between the respective Log-On Request and Log-On Acknowledge bursts.
| Log-On Time | 1825 | 0019 |
|---|---|---|
| BFO used as a reference (closest stable value, assume level flight) | 144Hz @ 1828:05 | 252Hz @ 0010:59 |
| Log-On Request BFO | 142Hz @ 1825:27 | 182Hz @ 0019:29 |
| Log-On Request C/No recorded at GES | 30.28 | 40.59 |
| Log-On Request Channel BER recorded at GES | 5 | 0 |
| Log-On Request Difference Frequency (from BFO reference) | -2Hz @ 1825:27 | -70Hz @ 0019:29 |
| Log-On Acknowledge BFO | 273Hz @ 1825:34 | -2Hz @ 0019:37 |
| Log-On Acknowledge C/No recorded at GES | 42.55 | 43.38 |
| Log-On Acknowledge Channel BER recorded at GES | 0 | 0 |
| Log-On Acknowledge Difference Frequency (from BFO reference) | +129Hz @ 1825:34 | -254Hz @ 0019:37 |
| Delta frequency between the Log-On Request and the Log-On Acknowledge bursts, plus time period | +131Hz over 7 seconds | -184Hz over 8 seconds |
Table 1.9D - Log-On Bursts