As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AIRCRAFT WAS GROUNDED: ON APPROACH TO DCA ILS FMA NORMAL WE DIDN'T INTERCEPT LOC MISSED APPROACH TRIED RNAV APPROACH WOULD NOT ARM. AIRCRAFT DIVERTED TO PIT AND DECLARED AN EMERGENCY. THE AIRCRAFT LANDED SAFELY IN PIT WITHOUT FURTHER INCIDENT. MAINTENANCE REPLACED #1 FLIGHT MANAGEMENT AND GUIDANCE COMPUTER (FMGC) PER AMM 22-83-34. A SATISFACTORY OPERATIONAL CHECK WAS ACCOMPLISHED.