Thread: AF447
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Old 12th Jun 2009, 04:22
  #1225 (permalink)  
Join Date: Jun 2009
Location: Austin, TX
Posts: 1
To Captain Crunch

(lapsed student pilot here, but lots of computerized embedded systems expertise)

Regarding the "The granularity of the data is very high" statement, I interpreted this as saying "We don't know if or how the ACARS system batches transmissions".

In communications systems there is an overhead associated with obtaining the channel to communicate data, and to maximize utilization of the channel its appropriate to make the overhead (from a overall channel perspective) as minimal as possible. So the ACARS system might not transmit a single notification as soon as it receives it from the onboard systems... Hypothetical: Upon getting a notification it could set a countdown timer for 2 minutes, and when that 2 minute timer expires it transmits the original notification and anything else it receives in that two minute period. This is perfectly acceptable given what ACARS is intended for, and makes the overall communications system more efficient, but it also means that: a) The timestamps might not reflect the *exact* moment something was detected, rather it's a close approximation to the time. and b) There might have been unsent notifications in the ACARS system that never got transmitted (even if the transmitter and antenna stayed intact all the way til the end)
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