Linux was a poor choice for an O/S if the US intended to keep the source code private. As you know, China is allowed to make free copies of Red Hat Linux, from here in the US, and legally rename it "Red Flag" in China. However, the US has so far rightfully limited the distribution of Joint Strike Fighter software, even denying rights to it from apparent allies that contributed to JSF development costs. Let's hope they're able to keep this software private as well, as has been typical with previous fighter plane designs, and don't face any complications by Linux's "GPL" license created by leftist Richard Stallman.
http://www.dailytech.com/article.aspx?newsid=1266&ref=y
Do you honestly think that the decision-makers in the gov't would've failed to consider that point? The only place that source code is going is to the vendor (who alrady has it) and the customer, if they want it. The customer happens to be the US, so they can classify it if they deem it appropriate.
The source code will not be PD, or even publicly accessible.