You're probably right. I worked for Lockheed in a facility that was ATC and MS2. I was on the MS2 side, but our program was ATC for NATO countries (war and peac

You're probably right. I worked for Lockheed in a facility that was ATC and MS2. I was on the MS2 side, but our program was ATC for NATO countries (war and peacetime operations). All of the ATC applications were built on Solaris running SPARC. Most of the developers were familiar with Linux at the time, this was back in the early 2000s. But even then many of the devs wanted to migrate the platform to Linux for a number of reasons. The cost and time, however, for acceptance testing on Linux would have eaten the budget alive. So instead pieces and parts that were readily accessible in Linux were ported to SPARC. I remember getting a new requirement for GPS time (previously the system had only used Rubidium oscillators) and working with one of the devs on getting OTS hardware working with the ported code. The further along the program went and newer features were added to the scope the more this happened. But everything in the UI was based on CDE and some SPARC specific libraries for the UI. The HMI was written in ADA. Since these systems have so many requirements just swapping out the OS would be a major overhaul and I'm not actually sure that Linux would even be the right choice.