Satellite data unit logs back on

At 18:25:27 UTC the Satellite Data Unit on 9M-MRO initiated a log-on to the Inmarsat Indian Ocean Region satellite — Handshake 1. A log-on (as opposed to a routine hourly handshake) typically occurs after the SDU has lost power and been restored. The official investigation judged this log-on “most likely due to power interruption to the SATCOM avionics,” without establishing why power was lost and restored. From this point Inmarsat recorded BTO and BFO on each subsequent signalling unit, which later defined the 7th-arc search geometry.