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Aircraft Data Decoding A forum to discuss decoding the various data transmissions such as ACARS, Mode-S, ADS-B, etc.

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Old 08-14-2014, 8:08 AM
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Default CPDLC messages ?

Hi, just wondering if anyone using multiPSK or similar can post a few examples of CPDLC messages here ? I'm curious what they look like.

Thanks
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Old 08-14-2014, 1:47 PM
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The info I've been able to find indicates that there is a test setup operating in one ATC sector in Europe.
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Old 08-14-2014, 3:02 PM
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I don't know about the North Atlantic system, but ours down here goes through the Inmarsat satellite - not much hope of intercepting any messages via that!

From Wikipedia...
Quote:
The FANS-1 system originally developed by Boeing, and Airbus as FANS-A, are now commonly referred to as FANS-1/A, and is primarily used in oceanic routes by widebodied long haul aircraft. It was originally deployed in the South Pacific in the late 1990s and was later extended to the North Atlantic. FANS-1/A is an ACARS based service and, given its oceanic use, mainly uses satellite communications provided by the Inmarsat Data-2 (Classic Aero) service.
The first aircraft I saw it on was the AirNZ 767's in the 90's but now it's on all the long haul stuff that goes through AKL and Brisbane - they still have to use the HF voice network for backup though but the controller usually says "continue on CPDLC" after the selcal check.
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Old 08-14-2014, 7:56 PM
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Besides being used in trans-oceanic airspace and parts of Europe, CPDLC is deployed in domestic airspace across Canada by NAV Canada, the ATC provider here. CPDLC messages are relayed by satellite, by VDL2 (136.975 MHz) and by HF (HFDL), in that order of network preference. (Obviously depending on what system the aircraft is logged into at the time.)

I have compared some internal ATC system message transactions exchanged with specific flights against VDL2 messages using MultiPSK to receive the 136.975 MHz data. They are not plain text.like other ACARS-type messages. Even the standard log-on "Welcome" message cannot be seen as plain text over the air.

Bob
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Old 08-14-2014, 8:36 PM
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Bob,

Thanks for the info.

Quote:
They are not plain text.like other ACARS-type messages. Even the standard log-on "Welcome" message cannot be seen as plain text over the air.
Any idea what the format is ? Hexadecimal ? I'm wondering if there is some way to decode it ? Maybe they use some sort of encryption protocol and I'm just wasting my time ?

I'm located close to a 136.975 transmitter and can hear the databursts, now I just have to figure out how to get multiPSK to work.

Do you have any examples handy you can paste here just so I can see what the multiPSK output is supposed to look like ? Or hints on receiving it ?

Thanks for any info.

DJ

FYI related NOTAMS from Toronto Center ....

A2772/14 NOTAMN
Q) CZYZ/QCDXX/IV/NBO/E /000/999/4729N08055W999
A) CZYZ
B) 1404121200
C) PERM
E) WEF 2014 APR 12 1300
CPDLC WELCOME MESSAGE WILL BE IMPLEMENTED IN TORONTO ACC.
TORONTO ACC WILL COMMENCE USE OF THE CPDLC WELCOME MESSAGE WITHIN
HIGH LEVEL AIRSPACE FL290 AND ABOVE. FOLLOWING A SUCCESSFUL CPDLC
CONNECTION WITH TORONTO THE FOLLOWING MESSAGE WILL BE SENT TO ACFT
VIA CPDLC:
UM169 - FREE TEXT 'THIS IS AN AUTOMATED MESSAGE TO CONFIRM CPDLC
CONTACT WITH TORONTO CENTRE'.
THE ATSU GROUND SYSTEM IN TORONTO IS EXPECTING A RESPONSE TO THE
WELCOME MESSAGE. UPON RECEIPT OF THE WELCOME MESSAGE AIRCREW ARE
REMINDED TO RESPOND WITH DM003 - ROGER

A4471/14 NOTAMR A2776/14
Q) CZYZ/QCDXX/IV/NBO/E /000/999/4729N08055W999
A) CZYZ
B) 1406091318
C) PERM
E) CZYZ WEF 2014 APR 12 1300
CPDLC PHASE 1, 2, AND 3 FOR TORONTO ACC IMPLEMENTED WITHIN HIGH
LEVEL AIRSPACE FL290 AND ABOVE AS PER AIC 15/14.
ONLY THE FOLLOWING DOWNLINK MESSAGES WILL BE SUPPORTED BY TORONTO
ACC:
DM0 - WILCO
DM1 - UNABLE
DM2 - STANDBY
DM3 - ROGER
DM4 - AFFIRM
DM5 - NEGATIVE
DM6 - REQUEST (ALT)
DM9 - REQUEST CLIMB TO (ALT)
DM10 - REQUEST DESCENT TO (ALT)
DM18 - REQUEST (SPEED)
DM20 - REQUEST VOICE CONTACT
DM21 - REQUEST VOICE CONTACT (FREQ)
DM22 - REQUEST DIRECT TO (POS)
DM28 - LEAVING (ALT)
DM29 - CLIMBING TO (ALT)
DM30 - DESCENDING TO (ALT)
DM32 - PRESENT ALTITUDE (ALT)
DM34 - PRESENT SPEED (SPEED)
DM37 - LEVEL (ALT)
DM38 - ASSIGNED LEVEL (LEVEL)
DM39 - ASSIGNED SPEED (SPEED)
DM47 - SQUAWKING (CODE)
DM55 - PAN PAN PAN
DM56 - MAYDAY MAYDAY MAYDAY
DM57 - (FUEL) (FUEL2) FUEL REMAINING (SOULS) SOULS ON BOARD
DM58 - CANCEL EMERGENCY
DM60 - OFFSETTING (DOFF) (DIR) OF ROUTE
DM61 - DESCENDING TO (ALT)
DM62 - ERROR (ERROR INFORMATION)
DM63 - NOT CURRENT DATA AUTHORITY
DM64 - (ICAO FACILITY DESIGNATION)
DM65 - DUE WEATHER
DM66 - DUE AIRCRAFT PERFORMANCE
DM67 - FREE TEXT
DM80 - DEVIATING (DOFF) (DIR) OF ROUTE
ANY DOWNLINK MESSAGE OTHER THAN THE ABOVE WILL GENERATE A 'MESSAGE
NOT SUPPORTED BY THIS FACILITY' RESPONSE FROM THE GROUND SYSTEM.
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Old 08-14-2014, 8:52 PM
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Snippets of some of the "plain test" text I was able to convert from HEX to ASCII, but nowhere near what an entire message would contain. We were looking specifically for the welcome message because we had exact transaction times stamps of log-ons to compare, but no joy.

Between the number of VDL2 ground stations, the relatively limited use of CPDLC in our airspace so far (Toronto ACC) and the fact that many of the exchanges will be via satellite at least in part, I haven't taken it any further so far. A winter project....

As for MultiPSK, there's considerably more characters compared to most conventional ACARS message but there is plain text to be seen. You'll know when you have it working as you'll see some words.

Here's a couple of VDL2 ground station (uplink) messages:

08/15/14 01:57:41 UTC
Destination address (hexa): A83E06 (Aircraft)
Source address (hexa): 1024FA (Ground Station, delegated address , command frame)
I (Information) frame N(R)=2 N(S)=1 P=0
ACARS message ("AOA")
Data (hexa): FFFF0132AECEB6B3B043DA1552C1DA02343820D0D6C4203131 0D8AB5B63838AD313420495220D0D6C42031310D8AD3C849D0 2034B6B3B0204554C420B0B6B0B04C0D8AB53831B920CDD3D0 203131204554C420D5CEC1D6C1494CC1C24C450D8A8329207F
Mode: 2 Identifier: N630CZ Ack.: {NAK}
Message type: RA (Uplink - Command aircraft transmit diagnostic) Block: Z
Message: 48 PVD 11
5688-14 IR PVD 11
SHIP 4630 ETD 0600L
5819 MSP 11 ETD UNAVAILABLE


and a Squitter:

08/15/14 01:59:31 UTC
Broadcast address (hexa): FFFFFF (All aircraft)
Source address (hexa): 1024FA (Ground Station, delegated address , command frame)
XID (Exchange Identification) frame F=0
Data (hexa): 8280001C0109383838353A3139393302020001030320848005 0207D8060207D8F0001F000156040120C3044359595AC40600 0000000000C504FC020000C8031B5CE4
Ground station (+/- 3'): 4342'N 07936'W

From an aircraft (downlink)

08/15/14 02:00:21 UTC
Destination address (hexa): 1035DA (Ground Station, delegated address)
Source address (hexa): A8856D (Aircraft airborne , command frame)
I (Information) frame N(R)=6 N(S)=7 P=0
ACARS message ("AOA")
Data (hexa): FFFF0132AECEB63438B0B915B5DA3102CDB3B9C1434F31B632 B63134CB45575220524551D545D35420C7C1544520C1D3D349 C7CECD45CE54204554C1B03234B58313BA7F
Mode: 2 Identifier: N64809 Ack.: {NAK}
Message type: 5Z (Airline designated downlink) Block: 1
Message: M39ACO162614KEWR REQUEST GATE ASSIGNMENT ETA0245:

Good luck!

Bob
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Last edited by ATCTech; 08-14-2014 at 9:01 PM..
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