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Old 4th Jun 2009, 00:25   #1 (permalink)
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ACARS Data Format

Much is (rightfully) being made of the ACARS transmissions from the Air France A330.

Is ACARS data encrypted?

If not, is the data format available to the public?

Is ACARS data the same for each type of airplane or do different airlines have different formats?
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Old 4th Jun 2009, 02:06   #2 (permalink)
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ACARS data sent over VHF is not encrypted and can be received with simple radio equipment. I don't know about ACARS sent over SATCOM or HF.

It is up to the airline what data is sent, but generally the formats are similar.
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Old 4th Jun 2009, 04:48   #3 (permalink)
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G'day Ed,

Google it mate, there are over 100,000 entries relating to ACARS scanning. Why you'd want to eavesdrop ACARS messages I don't know. Mostly sent by VHF when in range and SATCOM otherwise, never by HF as far as I know.

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Old 4th Jun 2009, 05:17   #4 (permalink)
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HF ACARS is now dead, replaced by SATCOM.

Anyone can scan the ACRS messages, which isn't a good thing IMHO. My last airline had an incident where a PDA was found in a seatback, evidently left from a previous flight. The crew ACARSed ops to say they found it. Some idiot spotter was scanning ACARS, saw the message and though it would be a joke to send a bomb phone hoax to the company saying a bomb was on the flight hidden in a PDA. Flight diverted mid Atlantic.

Idiot is still probably in prison. He got a long stretch!
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Old 4th Jun 2009, 06:12   #5 (permalink)
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ACARS is not encrypted. There are standards for many ACARS messages, they're available to anyone willing to pay ARINC (the ACARS inventor) to get them. Routing information (source/type/date if you will) is always standardized for automatic processing, data may or may not be standardized depending on its purpose.

Last edited by gtf; 4th Jun 2009 at 06:35.
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Old 4th Jun 2009, 08:33   #6 (permalink)
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HF ACARS is now dead, replaced by SATCOM.
Er, not quite! HF ACARS regularly used over the North Pole where (currently) there aint no satellite coverage.
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Old 5th Jun 2009, 18:10   #7 (permalink)
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ACARS is encrypted using williamsburg protocol and encapsulated by the service provider to match the protocol BATAP or something else.
there are prety good internet ACARS sites able to display the ACARS messages transmitted through VHF, these messages have been decrypted.
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Old 5th Jun 2009, 20:17   #8 (permalink)
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Just to clear a few things up regarding ACARS

It is normally sent over VHF - but can be sent via SATCOM.

ACARS over HF is far from dead! but has opened up new routes to some carriers as they are now able to maintain contact with flight ops in areas of the pole where there is no sat coverage.

The ACARS messages on the internet have not been decrypted merely decoded into a format that can be read by the enthusiast and not just the airlines software.

However the scanning of ACARS is likely to die out soon as ARINC have released a version of the software that will encrypt all of the information end - to end.

As of yet I'm not aware of any airlines that use this upgraded ACARS - if you go to the ARINC website you will find the information about why and how they are encrypting it.

PS. it is using digital encryption so no chance of the anoraks / other airlines having access to it in the future!

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Old 5th Jun 2009, 21:50   #9 (permalink)
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I've never flown an ACARS equipped aircraft but as far as I know the data "package" sent by the ACARS contains the actual FMC position info.
If its true that the investigators have an ACARS msg reporting certain system abnormalities they must have the attached POS info. They should have a pretty exact last pos to start SAR. But the inital search covered a wide area.
Any explanations?? (Perhaps the POS info was garbled? Or the airplane flew on for long minutes after the first sytem failures.?)
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Old 4th Jul 2009, 18:20   #10 (permalink)
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The airplanes installed with ACARS may have several functions:
1. The airplane installed with ACARS & activated FANS capability, this airplane is able to communicate ATC via ACARS (CPDLC function).
2. My company modifes ACARS software, let flight crews caculate V1/Vr/V2 via ACARS, and request & receive loadsheet, flight plan, send flight log etc..
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Old 5th Jul 2009, 06:29   #11 (permalink)
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an ACARS message does NOT include position. It include message ID, aircraft ID, checksum, send sequence, reply sequence, message type and subtype, and message data. the message data format is unique for every message type and subtype. every message is 220 characters or less in length. longer mesages are split up into "Multipart messages" and are limited to 3000 chars total.
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