Stallman and the FSF has fairly arbitrary views on this stuff. Non free firmware running on microcontrollers is fine because it's part of the hardware. But if there is a firmware blob that gets copied over by the OS on boot, then it's not ok for unclear reasons.

Results in a lot of stuff getting rejected for FSF certification despite being just as open practically as the certified stuff.

A car probably just isn't seen as software to him if it's just the internal control systems. Maybe the entertainment system these days would be.

I think what it means is that if there were open source airplanes he’d take those, even at the cost of an enormous detour.

RMS is notorious for his willingness to go through quite a lot of inconvenience to stick to his free software principles.

You can search his site for the word "ticket" to get an idea of how he feels about software systems in public transport.