I know, this seems a 'crazy' question, but someone knows which operating system is used for airplanes ? Thanks
Disclaimer: I gathered this information purely from google/wikipedia, I can't judge if it is actually correct but should get you started.
According to this document by Green Hills Software the FAA requires software on airplanes to pass the DO-178B, Software Considerations in Airborne Systems and Equipment Certification.
The Integrity operating system developed by that same company is apparently certified as such.
Off course most of this information is either from the company that sells this particular OS or from wikipedia. Use with care.
In the military such operating systems of course are not revealed to the public. In other applications, they are likely proprietary or closed source, and its details are not revealed to the public.
The essential characteristics of such an operating system, however, are described in the link above.
Since my work has me actually touching avionics and reading the specs, it depends on the device and the manufacturer.
This is one of those "Which metal is used to manufacture a car?" questions where the questioner thinks only Iron or Aluminum is the answer. Without specificity to device and manufacturer, no answer is possible except maybe "All of the ones used."