ACFT EQUIP PROB. PRESSURE LEAK FROM DOOR SEAL. ACFT DEPRESSURIZED SLOWLY AS RPTR PLT DSNDED FOR APCH AND LNDG.

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CRUISING AT FL370; A SLIGHT SQUEAL BEGAN SOMEWHERE NEAR THE CABIN DOOR. AFTER DETERMINING IT WAS THE DOOR SEAL LEAKING AIR; I ASKED AND RECEIVED A LOWER ALT FROM ZID AND ALSO STATED THAT I WAS EXPERIENCING A PRESSURIZATION PROB. AROUND FL310 THE SQUEAL BECAME LOUDER AND I THEN DECLARED AN EMER AND STATED TO ZID THAT I WAS HAVING A DOOR SEAL FAILURE. I WOULD LIKE TO EXTEND MY SINCERE COMPLIMENTS TO THE ZID CTLR AND CINCINNATI APCH CTLR FOR THE WAY THEY HANDLED THE FLT UNTIL I HAD LANDED SAFELY. THE CREW AND PAX WERE PREPARED FOR RAPID DECOMPRESSION; BUT I THINK THE ONLY REASON IT DID NOT HAPPEN UNTIL MUCH LOWER ALT WAS THE FACT I WAS ABLE TO KEEP ENG THRUST AROUND 88-90 PERCENT; WITH SPD BRAKES DEPLOYED AND A DSCNT OF 4000-5000 FPM. THE CABIN DID NOT COMPLETELY DEPRESSURIZE UNTIL DSNDING THROUGH 12000 FT FOR 8000 FT. THE 10000 FT CABIN LIGHT APPEARED ONLY FOR ABOUT 10 SECONDS. THE OUTCOME OF THIS EMER WAS MUCH BETTER THAN WHAT COULD HAVE HAPPENED. I CANNOT REMEMBER EVEr DEVIATING FROM AN ATC CLRNC DURING THIS EMER; BUT I AM SUBMITTING THIS RPT AS A PRECAUTIONARY MEASURE. WITH PREPARING THE CABIN FOR A POSSIBLE DEPRESSURIZATION; FLYING THE AIRPLANE; PLANNING FOR THE WORST; COMMUNICATING WITH ATC IN A NOISY ENVIRONMENT; A PLT NEVER KNOWS WHEN AND IF HE MADE A MISTAKE.