As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
FLT 6338 - IAD-SYR - DURING CRUISE, AIRCRAFT MADE AN UNSCHEDULED LANDING DUE TO F/O'S ADI PRECESSING IN FLIGHT. AIRCRAFT RETURNED GATE WITH NO FURTHER PROBLEMS. MAINTENANCE INSPECTED AND REMOVED AND REPLACED ADI, OPS CHECK OK. AIRCRAFT WAS RELEASED AND RETURNED TO SERVICE. (M)