As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
BOS - FLT 4596 - DURING TAXI CREW REPORTED SMOKE IN COCKPIT BUT NOT IN CABIN. AIRCRAFT WAS RETURNED TO THE GATE. MAINTENANCE COULD NOT DUPLCIATE DISCREPANCY. A GOUND ENGINE RUN WITH BOTH ENGINES AND BOTH PACKS OPERATING WAS SATISFACTORY WITH NO SMOKE NOTED. AIRCRAFT WAS RETURNED TO SERVICE. (M)