Did you actually read my post? If yes, can you seriously not see the difference between writing/testing an OS and writing/testing the software that controls jet engines?
Open sourcing something like Linux works very well _precisely_ because it has a very large audience and is (relatively) approachable by hobbyists too.
On the other hand, aerospace engineering and software is narrowly specialized with a (relatively) small group of experts and code used in commercial/military aircraft is anything but approachable to hobbyists.
Then there is the fact that unit testing this kind of code requires engineering knowledge of the specific hardware involved (e.g. not just any jet engine, but one very specific model). Finally, let us not even mention the huge pink elephant in the room, namely that the absolute and vast majority of "hackers" does not have access to jet engines used in commercial (or military) airplanes and even fewer have the ability to conduct test flights.
I mean, who would fix problems if it's just a hobby? And if it's open, it must be a hobby. Surely, that can't possibly work!