Hi Neil
how are you trying to decompose the track files ?
I already have a TCL parser if that would help ?
anyway the format is pretty simple, you have
$GPxxx - NMEA Messages
$PFxxx = Flarm Messages
Additionally you will see
$PAxxx - PAW messages
These are diagnostic, or provide tagged information to better understand the FLARM messages
for example
$PAWRT,4B19D1,1,1,1,1,0,0,*4B
This says the ICAO/Code 4B19D1 is transmitting
1,1,1,1,0,0
Mode-A, Mode-C, Mode-S, Mode-S/ES, PilotAware, Flarm
you will also see
$PALOG,FF4440,AUDIO,MODEC,,,222*75
$PALOG,4787B2,AUDIO,GPS,9.99,1043,191*13
$PALOG,4AC8B3,AUDIO,MODES,,,162*19
This indicates what messages were passed out to the audio
Hope that helps