acarcode.hlp
Dear Reader.

Here again is some additional information that may
help you to understand and decode the ACARS messages. 



Acars message contents:

	======MESSAGE NUMBER FIELD======

Msg.No 1205 	(this indicates that this message is 
		transmitted at 12.05 past the hour)

Sometimes the Msg No. is preceded with a letter for 
the first character, this indicates that the message 
is send automatically by one of the boardcomputers, 
or data acquisition units. The first letter does 
indicate the type of which Avionics Unit the message 
originates from.
 
1. The Flight Management Computer 		FMC
2. The Combined Fault Data Indicator Unit	CFDIU
3. The Digital Flight Data Acquisition Unit	DFDAU

Message Sequence Nr #	Avionics Unit originating Message

COOO - C999		CFDIU		   
D000 - D999		DFDAU
F000 - F999		FMC


Messages from the DFDAU can contain Engine and/or Aircraft 
Performance data, and the FMC will often contain the flight 
plan, most of these messages are found in the H1 Message 
label. Sequence number prefixes such as "M" and "A" 
and sequences that drop the leading minutes digit are 
often observed, these are caused by aircraft Avionics type
differences.


   ====== H1 OPTIONAL AUXILIARY TERMINAL MESSAGE ======


These messages are used to transmit various flight and/or 
engine performance data and navigation and other parameters.
It seems that different airlines use different formats and 
codes.

The H1 message usually reflect data dumps from the Fligt
Data Recorder "DFDAU", the Fligt Management Computer "FMC"
or the Central Fault Data Indicator "CFDIU". 
All these messages begin with a crosshatch "#" character, 
the two characters indicate the data acquisition unit 
(black box) from which the data came from.

CF = CFDIU, DF = DFDAU, M1 = FMC, M2 = FMC, these 
characters will be consistent usually with the first letter
of the message sequence number. In the case of the FMC 
either an M1 or M2 will be shown in the first and second 
characters to indicate which of the onboard flight com-
puters data is transmitted. The third character is an
A or a B to show wheter the message is in the conventional
or conversation mode.    

Examples

#CFBFLR  or #CFBWRN	Equipment Failures
#DFB*TKO or #DFBTKO	Take Off Performance data
#DFB*CRZ or #DFBCRZ	Cruise Performance data
#DFB*WOB or #DFBWOB	Weather Oservation 
#DFB/ PIREP		Pilots Report
#DFBEDA  or #DFBENG	Engine Data
#M1AAEP			Position/Wheather report
#M2APWD			Flight plan Predicted Wind Data
#M1BREQPWI		Predicted wind info request  	 

Example:

[25/01/1996 22:50]
ACARS mode: H  Aircraft reg: .G-xxxc
Message Label: H1 Block Id:9 Msg. no. C09B
Flight Id: VSXXXX
Message content:
#CFB20015 GEN 3 ELEC Fault...... etc. ete. 	 
|   |	  |	
|         | Generator no 3 has electrical problems.
|
|Equipment Failure from 
 Combined Fault Data indicator Unit CFDIU 

		
This flight Transmitted Msg. no's C09A tru C09F,
each message contained different equipment failures,
ranging from clogged galy lavetory duct,tripped
circuit breakers, inoperative radar antenna, smoke,
APU fuel pump failure etc. etc.
Eventualy followed by a urgent request fo a fligtplan
below FL300.

For obvious reasons the fligt number and Airline are 
are not disclosed.

Glossary:
Avionics	Aircraft electronis
APU		Aux Power Unit
FL300		Flight Level 300.000 ft (10Km approx).



NOTE

I have noticed that many  Airlines use other letter codes
in the chracters trailing the '#" characters
Does anyone know the explanations other than those listed 
above?
I do appriciate any additions to this list, I will compile
any information recieved on this the subject, and i will
make it public in the next revisions of acarshelp.zip and 
acarsort.exe. With your much appriciated help Acarshelp 
will become a living document.


References
various publications from	:Arinc
				:AEA
				:PA0DAL
				:Lowe
				:Jeppessen Publications
				:Universal Radio Research					
			   	: 

Good luck and happy decoding

Bert van Dalen PA0DAL @ PI8UTR  