As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
FLT 6455 - IAD-PHL - DURING TAXI, THE FLT EXPERIENCED A FLAG ON THE FIRST OFFICERS HSI. AIRCRAFT RETURNED TO THE GATE WHERE MAINTENANCE TROUBLESHOT AND REMOVED AND REPLACED THE FIRST OFFICERS GYRO. ALL CHECKS WERE ACCOMPLISHED AND THE AIRCRAFT WAS RELEASED FOR SERVICE. (M)