Had a nav system go dead right after a pit stop in Dallas
Was finishing up a pit crew check on a regional jet. Everything looked good on the ground test. The plane pushed back, then the captain called back immediately. Said the whole FMS screen was black. No route data, nothing. My stomach dropped. Ran back out with the tow crew. Found a main avionics cooling fan had failed quietly. Overheat warning didn't trip fast enough. Had to pull the whole unit, swap in a spare, and reload the database from our truck. Took about 90 minutes. Captain was cool about it, but it was a close one. Ever had a cooling fan fail without the usual warning signs?