Originally Posted by
Shadoko
"Raw data PDF": 18:25 - Log-on Request, initiated from the aircraft terminal. This is the end of the link lost period that began at sometimes between 17:07:48 and 18:03:41.
What it the meaning of that?
- a trick (before turning South) from somebody who handled the a/c knowing it had have to be "viewed" on a west route?
- an automatic sat link after HF was available along the route above Malaysia and lost again?
- some automatic data Tx from a so big change in flight caracteristics it had to be "signaled" for frequency or BFO adjustment between sat and a/c?
- ... ?
It would be interesting to know what were the subsequent "user data".
If the system was not responding to interrogations at 18:03 and it initiated a logon at 18:25, the logical conclusion is that it was physically shut down from the cockpit at some point prior to 18:03 and then (possibly unintentionally) turned back on at 18:25.
The interesting question is what would have caused it to come back on. Perhaps the aircraft was flown manually between 17:21 and 18:25 and the pilot turned on the autopilot to continue the route via waypoints at 18:25.
"User data" may be part of the standard logon procedure for this aircraft, you see the same two packets at 16:01:16.
Side note: It looks like attempts to call the aircraft at 18:39 and at 23:13 had the side effect of resetting the interrogation timer, which is why we see handshakes at 19:40 and 00:11.