A/C Packs....


Well-Known Member
Would any of the big-iron drivers care to bore us with an in-depth explanation of the A/C packs on transport category aircraft, and maybe a web link with some diagrams? Maybe scan some junk out of a manual? Would be appreciated!!!


Well-Known Member
I'm sure this has been posted in another link. At Midway, PAC stood for Pressurized Air Controller in one manual and Pneumatic Air Cycle Machine in another.

It's basically an advanced air cycle machine.

Here is a site with some pretty good pictures and diagrams:



Let us also not forget the epic "Pressurization ACM" thread in the Tech/Ops forum over at airliners.net. It had a steady body count going for more than two months, with guys scanning pages from maintenance manuals and crawling in the guts of jets with a digital camera.

Education + Entertainment (+plus that site) = Edutainment (at its most awkward moments)


Well-Known Member
Packs are a pretty simple concept, really. Air is compressed, and due to compression it gets hotter than it already was. The hot air is put thru a radiator of sorts, where it is cooled by outside air that is moved thru the radiator with fans on the ground or airspeed in flight. This cools the air to a relatively lower temp. The air then goes thru a turbine which decompresses it, and in that process it cools to a lower temp than it started out with. The process is not so much different than a katabatic wind, really.