As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
PHL - FLT 346 - AFTER TAKEOFF THE CREW REPORTED THAT EVERYTIME THE STAB TRIM SWITCH WAS ACTUATED FROM EITHER YOKE, THE FIRST OFFICERS HSI HEADING FLAGS APPEARED. RELEASING THE SWITCH CAUSES THE FLAGS TO DISAPPEAR. DECISION WAS MADE TO RETURN TO FIELD AT PHL. FLIGHT LANDED WITHOUT FURTHER INCIDENT. NO EMERGENCY WAS DECLARED. MX R & R THE NR 2 COMPASS TRANSFER RELAY. OPS CHECK NORM. (M)