Many thanks for this thorough explanation! That's exactly what I was after.
The details you provided show you are very knowledgeable, perhaps you would be able to comment on some of the following messages and where I might find IAS/Mach/Heading information?
The reason I'm interested in this is because when combining these three parameters with the concurrently received ADS-B info, I can calculate the weather components for the slice of atmosphere where the airplanes are travelling near my site of interest. This could provide some very valuable improvements to the forecast and nowcast models which our observations are dependent upon.
The first type I see a lot of are DFB messages sent in triplets. I read that DFB means they originate from the digital flight data acquisition unit. They're all H1 labelled messages (again I'm not including the ACARS header info for privacy) so they're likely custom formatted for the airline in question. There's some position information in there, (S2327 E11648 in the third message) and, I hope, there's a IAS/Mach/Heading entry hiding as well. I've X'ed the routing info that was in the message.
#DFB/AEPR.
PRF/41A01
55054100216112948001917XXXXXXXX1701002455000
3599507482467-181085760-438000011000001101124
138715431622138708390875062002114001990008513131
13861543162313840840087406290206700191000851
Block End
#DFB3276
09309800803300478-1791286046506700329
09209900703300478-1791292046706720331
025802590000-00103450738156180062173
026302630000000103530713089090063308
0006120000000006010000000000000000700000
0006
Block End
#DFB020000000006230000000000000000100000
4505178200091791-001900060019S2327E11648
-017-01500030002000100010008-009-007
-015-013-0040002
00962-00280004105664007540072604400
Following is another type I see many of (X'ed the aircraft registration). This is a ADS position report (if the ADS tag and message type aren't lying) addressed to Melbourne Centre that however appears to be scrambled, I've seen quite a few of those messages. Looks like a hex encoded bitstream. before I sink my cryptographic teeth into this, any clue how that's encoded?
/MELCAYA.ADS.XX-XXX07EEEF7A91DE0996D6F01D0E2FE8F7004010060A3E760DEE35429851C 9980282ED1412A6E4899800F822