The inclusion of the .air file as part of the construction of an aircraft model is something of a mystery.

As mentioned earlier, it contains the elements that construct the flight dynamics of the aircraft. There are a lot more entries in the .air file than in the aircraft.cfg.

I assume that these are things that Microsoft considered users would never want to change for some reason. (They got it well wrong with reverse thrust power).

Where entries appear in both the .air and the aircraft.cfg, the aircraft.cfg file takes priority.

In most instances, there's no need to access the .air file except where there isn't an equivalent entry in the aircraft.cfg.

Finally, it's worth noting that I'm sure there is nothing in the .air file that can't be reproduced in the aircraft,cfg file as an entry. I found the parameters when downloading the Panels & Gauges SDK.

Why Microsoft chose to have a .air file at all remains the mystery.

I think your knowledge of the history provides the explanation here.

I'd presume that the retention of the .air file might be based on on retaining backwards compatibility with old aircraft.

Or perhaps the remaining employment of someone at Microsoft who likes working with them. 

I really doubt they would tell us

Hi Liran,
there is a site with a lot of .air file support you can go to and with links to the .air support board where you will get answers to all your questions there.

Air File Editors
http://perso.wanadoo.fr/hsors/FS_Soft/fsairfile.html

Air File Board, post March 2003
http://www.avhistory.org/scripts/MegaBBS/logon.asp

The .air file is not in ASCII but you can dump it and read it using AirUpDate program. The decode of the numbers is in AirEd.ini and there are 2 good editing programs that you can tune aircraft flight preformance with.

HTH
Ian