As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
BLOCK TURN BACK, DUE TO SMOKE IN COCKPIT APPEARS TO BE BLEED AIR SMOKE. NR 3 PACK VALVE CLOSED ACM OUTLET TEMP 85 DEGREES C, NO TRIP. SUSPECT SMOKE CAME FROM CONTAMINATED AIR DUCT AND DUE TO ACM NR 3 ABOVE 85 DEGREES C. PERFORMED OPS TEST, AIR CONDITIONING PACK AS PER AMM 21-51-00, FIND ALL NORMAL. REMOVED AND REPLACED PACK NR 3 FLOW CONTROL VALVE AS PER AMM 21-51-03 AND PERFORMED PACK OVERHEAT SYS TEST PER AMM 21-51-00. FOUND ALL SATISFACTORY.