Narrative:

During cruise flight; at an altitude of FL310; the first officer and I noted a strange noise coming from the main cabin door. Over the next min the noise became so loud the first officer and I could hardly hear each other. The cabin altitude was starting to climb. We decided we needed to execute an emergency descent. As a precautionary measure we donned our oxygen masks. I initiated the emergency descent and changed the transponder squawk to 7700 while the first officer called center to declare an emergency and do the emergency checklist. The cabin ascended to approximately 8000 ft to 10000 ft. We diverted to ZZZ and executed a normal ILS approach and landing.

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Original NASA ASRS Text

Title: A P180 IN CRUISE FLT EXPERIENCED LOSS OF CABIN PRESSURE. THEY DECLARED AN EMERGENCY; DESCENDED; AND DIVERTED TO THE NEAREST SUITABLE AIRPORT.

Narrative: DURING CRUISE FLT; AT AN ALT OF FL310; THE FO AND I NOTED A STRANGE NOISE COMING FROM THE MAIN CABIN DOOR. OVER THE NEXT MIN THE NOISE BECAME SO LOUD THE FO AND I COULD HARDLY HEAR EACH OTHER. THE CABIN ALT WAS STARTING TO CLB. WE DECIDED WE NEEDED TO EXECUTE AN EMER DSCNT. AS A PRECAUTIONARY MEASURE WE DONNED OUR OXYGEN MASKS. I INITIATED THE EMER DSCNT AND CHANGED THE XPONDER SQUAWK TO 7700 WHILE THE FO CALLED CTR TO DECLARE AN EMER AND DO THE EMER CHKLIST. THE CABIN ASCENDED TO APPROX 8000 FT TO 10000 FT. WE DIVERTED TO ZZZ AND EXECUTED A NORMAL ILS APCH AND LNDG.

Data retrieved from NASA's ASRS site as of January 2009 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.