What was found
N48PL HAD AN RTO ON 12-21-2023. WHEN I GOT TO THE PLANE THE FLAPS WERE AT FLAPS 20, FLAPS COULD GO BACK TO THE FULL UP POSITION, BUT THEY WOULD NOT GO PAST 20 DEGREES, I WAS ABLE TO SEE THE FLAP FAIL CAS MESSAGE, I INTERROGATED THE CMC, I FOUND A BIT TEST FAILED ON THE FSECU, ONCE THE FSECU SENSES THE FLAPS FAILED, THE FLAPS WILL STAY ON THAT SPECIFIC CONFIGURATION, UNTIL THE POWER IS CYCLED. I PERFORMED A GENERAL VISUAL INSPECTION OF THE FLAPS FOR ANY ABNORMAL MECHANICAL FAILURE, NO FAULT FOUND. I SHUT DOWN THE APU & TURNED ELECTRICAL POWER OFF FOR 10 MINUTES, HAD THEY CREW PERFORM A HIGH-SPEED TAXI TO RECREATE THE CONDITIONS OF THE FAILURE, EVERYTHING WORKED. PLANE FLEW TO KSAN YESTERDAY AFTERNOON WITHOUT ANY FURTHER ISSUES.