Last ACARS transmission

ACARS on 9M-MRO sent its last successful report at 17:07:29 UTC, a routine engine and performance snapshot via the satellite data unit. Subsequent scheduled ACARS messages at 30-minute intervals were not received. Ground-station messages at 18:03 and 18:05 UTC went unanswered, indicating the SATCOM/ACARS path was lost sometime between 17:07 and 18:03. The safety investigation later treated the loss of ACARS together with the near-simultaneous loss of transponder and VHF as a coordinated communications dropout, more readily explained by systems being switched off or unpowered than by a single random failure — while still being unable to prove who acted, or whether a failure mode not yet identified was responsible.