Press release says …
https://lynx.com/lynx-mosaic-selected-for-f35-lightning-ii-mission-systems-avionics
… yes. So: maybe.
It used to be an operating system named Integrity by Green Hills Software. That has its own Wikipedia article, too.
@alex_p_roe @timo21 I hate to break it to you, but the OS inside a fighter jet's gubbins probably isn't anything consumer-visible: it'll be some exotic micro-kernel RTOS written for high reliability and security that none of us have ever heard of.
Or it could be buzzword-compliant, be industry group certified, be originally developed for the Atari ST, have its own Wikipedia article, and run on (among other things) PowerPC. (-:
https://lynx.com/products/lynxos-178-do-178c-certified-posix-rtos