ERA10IA285 · Cessna 560XL

After concluding the preflight safety briefing for the passengers, the first officer closed the cabin door. The first officer remembered rotating the door locking handle but could not recall the direction he rotated it. He also could not recall looking at the cabin door lock indicator lights or the cockpit indicator, as was required by the operator's preflight checklist. Just after takeoff, the captain recalled that he heard the cabin door "leaking" and the first officer observed that the DOOR SEAL/CABIN DOOR annunciator lights were illuminated. When asked, the first officer did not recall the MASTER CAUTION annunciator illuminating. Had the MASTER CAUTION annunciator illuminated, it would have been one indication that the door was properly secured prior to the takeoff. While on the downwind leg of the traffic pattern during the return for landing, the main cabin door opened. The crew subsequently declared an emergency, and landed uneventfully with the main cabin door open. The airplane incurred minor damage during the landing and the passengers and crew were not injured. Postincident examination of the door and its locking and indicating mechanisms revealed no evidence of any mechanical malfunctions or failures. Because of the close proximity of the amber-colored CABIN DOOR annunciator light and the white-colored GROUND IDLE annunciator light, it is possible that the flight crew inadvertently overlooked the illuminated CABIN DOOR annunciator light prior to takeoff.

Verbatim NTSB analysis and probable cause from the NTSB dataset