HN39 has raised an interesting point regarding the sequencing and 'dead' time slots in the time apparently available, i.e. up to the handshake received back on the aircraft following the last message.
As a short refresher, here are the ACARS messages as time-stamped to the nearest minute, along with their receipt times:-
An interactive web page with the above list is available from
here. You can highlight one or more lines by clicking on them, and clicking again will return the line to normal.
Below is a revamped version of how the BEA described what was displayed in the cockpit, and what wasn't.
Notes:
- The ACARS time stamp has been given a different background color for each minute.
- Warning messages take precedence over Fault Reports, and the 0210 position report had overall precedence in the ACARS sequence.
- Sequencing within the FMS of the AOC messages is not precisely known.
- The receipt timing (not provided by the BEA) of the 0200 position report in the ACARS system will provide a good indication of when the 0210 report was probably ready in the FMS to be inserted into the AOC sequence.
- Highlighted cockpit effect messages are secondary faults, i.e. not causative.
- The note associated with TCAS cockpit effect message has been inserted by me (from BEA Interim Report No.2).
The gaps in the message sequencing are for either of the following reasons, i.e.
- there was no AOC traffic queued in the FMS,
- data corruption required a retransmit,
- loss of data link.
Total time for each message was approximately 6 seconds, which comprised synchronization, message header, data and receipt confirmation.
Finally, for those that remember the old Telex/Teleprinter systems, the
ACARS protocol was a product of that time, and the data transmission speeds are similar.
mm43