Narrative:

After takeoff and on climb out at 9;500 ft; we experienced the illumination of the cabin attendant altitude hi annunciator we informed ATC that we needed to level at 10;000 ft and did so. After running checklist and consulting with dispatch and maintenance control they determined we could continue the flight at or below 10;000 ft. We agreed that we could still accomplish the flight. Then shortly after the aircraft became very loud and began shuddering. My first officer pressed the annunciator test button and the cargo door annunciator was not illuminating. I pushed the annunciator and it illuminated indicating the cargo door was open. We decided returning to the departure airport was the best option. We ran appropriate checklists; declared an emergency and slowed the aircraft to 140 KIAS. At that speed the shudder of the aircraft was lessened we also informed dispatch of our return. No other abnormalities occurred during the return and landing. After exiting the runway we stopped just after clearing the runway and were informed to shutdown. A mechanic was there and secured the door at which point we determined it was safe to continue to taxi to the gate and de-board the passengers there. After returning to the gate we began making calls to dispatch; maintenance; chief pilot and director of operation. Going back to the start of the flight I remember the all the annunciators working correctly from the acceptance.

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Original NASA ASRS Text

Title: A BE-1900 CAB ALT HI alerted at 9;500 FT while climbing so the aircraft was leveled at 10;000 FT and the checklist completed. Shortly thereafter; the cargo door opened so an emergency was declared and the flight returned to the departure airport.

Narrative: After takeoff and on climb out at 9;500 FT; we experienced the illumination of the CAB ALT HI annunciator we informed ATC that we needed to level at 10;000 FT and did so. After running checklist and consulting with Dispatch and Maintenance Control they determined we could continue the flight at or below 10;000 FT. We agreed that we could still accomplish the flight. Then shortly after the aircraft became very loud and began shuddering. My First Officer pressed the annunciator test button and the cargo door annunciator was not illuminating. I pushed the annunciator and it illuminated indicating the cargo door was open. We decided returning to the departure airport was the best option. We ran appropriate checklists; declared an emergency and slowed the aircraft to 140 KIAS. At that speed the shudder of the aircraft was lessened we also informed Dispatch of our return. No other abnormalities occurred during the return and landing. After exiting the runway we stopped just after clearing the runway and were informed to shutdown. A Mechanic was there and secured the door at which point we determined it was safe to continue to taxi to the gate and de-board the passengers there. After returning to the gate we began making calls to Dispatch; Maintenance; Chief Pilot and Director of Operation. Going back to the start of the flight I remember the all the annunciators working correctly from the acceptance.

Data retrieved from NASA's ASRS site as of July 2013 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.