What was found
DURING CLIMBOUT, AT 12000 FEET, THE AURAL WARNING LIGHT ILLUMINATED FOLLOWED BY THE ILLUMINATION OF THE LEFT DUCT LEAK LIGHT. THE CAPTAIN FOLLOWED THE QRH PROCEDURES WHICH INCLUDED THE SECURING OF THE ENGINE. THE DUCT LEAK LIGHT EXTINGUISHED. AN EMERGENCY WAS DECLARED. SINGLE ENGINE PROCEDURES WERE FOLLOWED BY THE CAPTAIN TO RETURN AND LAND SAFELY. MAINTENANCE RAN THE LEFT ENGINE AND INSPECTED THE LEFT INBOARD DUCT AND OVERWING DUCT FOR LEAKS. OPERATIONAL CHECK WAS NORMAL AND NO LEAKS WERE FOUND IN THE DUCTS. AIRCRAFT OK FOR SERVICE.