Southwest Airlines, one of the largest airlines in the United States, was not affected by the Windows outage that disabled millions of computers worldwide because it uses an older version of Windows.

Most airlines in the US had to suspend their flights because the problem affected their servers and computers. However, Southwest Airlines avoided the problems and there turned out to be a salvation… Windows 3.1. Lately we often learn that different companies or institutions in different countries of the world are using either very old data carriers or old operating systems.

Windows 3.1 was released in 1992, so this is clearly a unique case. Southwest uses Windows 95 in addition to Windows 3.1 for its employee scheduling system. Southwest Airlines is probably not the only company to survive a crash due to very old software, but this is the only known case to date. Source