Southwest Airlines, the fourth largest airline in the US, is seemingly unaffected by the problematic CrowdStrike update that caused millions of computers to BSoD (Blue Screen of Death) because it used Windows 3.1. The CrowdStrike issue disrupted operations globally after a faulty update caused newer computers to freeze and stop working, with many prominent institutions, including airports and almost all US airlines, including United, Delta, and American Airlines, needing to stop flights.
Windows 3.1, launched in 1992, is likely not getting any updates. So, when CrowdStrike pushed the faulty update to all its customers, Southwest wasn’t affected (because it didn’t receive an update to begin with).
The airlines affected by the CrowdStrike update had to ground their fleets because many of their background systems refused to operate. These systems could include pilot and fleet scheduling, maintenance records, ticketing, etc. Thankfully, the lousy update did not affect aircraft systems, ensuring that everything airborne remained safe and were always in control of their pilots.
Just because it doesn't have TCP/IP doesn't mean there isn't networking. Networks existed before the Internet and its Internet Protocol after all. It wouldn't be so much air gapped as so archaic that only the most targeted attacks would work, and only if there is an infected PC acting as an intermediate between the Internet and ye olde network. Chances are it was never connected to the modern Internet as the technologies just aren't compatible.
Old doesn't mean secure. Those old systems have had decades since the last security patch. Even then computer security was barely a consideration for the developers.
I am not saying it is, normally old systems are the least secure. The bit you're not getting is that this system is almost certainly air gapped, just not by choice. It can't work with modern networks. It can't work with modern viruses. Any exploit a modern hacker would think to use probably doesn't exist yet. It's a bit like trying to break someone's car by putting sugar in the fuel, except they ride a horse. Do you get it yet?