Too bad they didn’t choose an American bird and original American software.
If you mean "Too bad they didn't choose Windows", that's easy -- think of the potential lawsuits due to viral cross-infection, data security breaches, etc. that would be possible with business people using essentially "public" Windows machines.
If you mean "Too bad they didn't choose Unix", probably it was the lack of common software apps.
If you mean "Too bad they didn't choose Mac OS X", I agree completely -- but probably Apple wouldn't sell them the necessary custom hardware components required to make Mac OS X work in non-Apple hardware. I'd love to see Apple license OS X for a wider variety of hardware, even if it all stays proprietary.
But given the above, Linux is the obvious choice.
too expensive. How often are they supposed to work on their airplanes, and how big does the tech support department need to be?
I know I’d have made the same choice, just install it and forget it.
To mess up a Linux box, you need to work at it; to mess up your Windows box, you just have to work on it