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Old 23rd Apr 2011, 04:39
  #3837 (permalink)  
Bizman
 
Join Date: Mar 1999
Location: Australia
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ACARS as an alerter?

There has much recent discussion regarding why ACARS was not referenced earlier re the loss of AF-447. Also, much discussion early in the thread on better design of DFDR/CVR boxes and pingers.

While acknowledging that ACARS is not designed to be anything other than an automated maintenance events log transmitter (and not necessarily exactly sequenced), one result I look forward to out of BEA's final report will be a recommendation that a new feature be implemented in airborne ACARs software and ground receiving computer systems:

1. Airborne ACARS to transmit a simple short standardised "I-am-alive-and this is my gps position altitude and heading" message every say 5 or 10 minutes. If the traffic overhead is low, it could perhaps be done every minute.
2. Ground based receiving computer systems to implement an automatic message parsing function to look for the I-am-alive message and trigger an alert if the next expected one or several messages are missing. The trigger could have a relaxed timing window to allow for the I-am-alive message to be pre-empted by routine maintenance messages taking priority.

This seems such a simple thing to do in software. May take months to years to certificate of course (on the airborne side, but not on the ground systems, particularly as ACARS likely does not have raw heading, position and altitude data routed to it), but would have the effect of:

a). Aiding airline dispatchers to raise an early initial alarm, rather than wait for ATC to coordinate of reports of missing scheduled communications.
b). Ensuring search resources can be mobilised faster, with greater certainty to a smaller search area.

ACARS is not designed for this function, but it is the one reliable system we have on board today that could be readily adapted to include this capability, having continuous immediate access to reliable global communications.
The ground based message parsing and triggering would be relatively trivial to implement.

Such a capability, could be relatively easily developed, requires no more boxes or systems in the aircraft, and may not even require any wiring changes if the (optional, preferably desirable,) gps position, altitude and heading data are available on any of the data buses brought to the ACARS system.

NB: This concept is much much different from suggestions way back early in this thread that FDR data be transmitted over ACARS. This would require high bandwidth, which ACARS does not support.

What I am suggesting is an ESSENTIAL requirement for ONLY for a standardised, very terse, I-AM-ALIVE code. Loss of one or several sequential messages is what would trigger an alert.

Any other data transmitted could be optional, depending on aircraft configuration and data availability to ACARS. I am suggesting only position, heading and altitude as minimally desirable, as together they enable a reasonably accurate estimate of LKP. VS/TAS/GS could be roughly and sufficiently interpolated from this, particularly if transmissions at the one minute or so level could be supported.
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