As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
FLIGHT 5588, CLE TO SDF. ON CLIMBOUT WHILE PASSING THROUGH 12,000 FT, THE FLIGHT CREW NOTICED A LIGHT HAZE ACCOMPANIED BY THE FAINT SMELL OF SMOKE. MEMORY ITEMS WERE FOLLOWED AND THE FLIGHT PREPARED TO RETURN TO CLE. ALL APPLICABLE CHECKLISTS WERE FOLLOWED AND THE FLIGHT LANDED WITHOUT INCIDENT. WHILE INSPECTING THE AIR CONDITIONING PACKS, THE ACM FOR THE NR 1 PACK HAD SEIZED. THE PACK WAS DEFERRED AND THE ACM WAS REPLACED ON THE 23RD. (A)