As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DCA - CREW REPORTED LEFT INERTIAL REFERENCE SYSTEM FAULT LIGHT ILLUMINATED IN FLIGHT. EMERGENCY DECLARED FLIGHT LANDED DCA WITHOUT INCIDENT. AIRCRAFT REMOVED FROM SERVICE. REPLACED LEFT INERTIAL REFERENCE UNIT. SYSTEM GROUND CHECK NORMAL OPERATION.