CEN15TA035 · Bell UH1H

Before the accident flight, the flight crew completed a routine law enforcement patrol flight without incident. That flight was conducted with the pilot, copilot, and main cabin quarter doors removed and the sliding main cabin doors in the "full open" position. After refueling the helicopter, the flight crew conducted a preflight inspection, during which, the copilot and a tactical team member (TTM) noted that the door latch pin was missing from the left sliding door latch. The TTM stated that the copilot advised him that the pin was not required to be installed. The copilot stated that he informed the pilot about the missing pin but that he was not sure that the pilot adequately understood him. About 15 minutes after departing, during cruise flight, the flight crew heard "a loud bang," and the pilot felt a momentary upset in the helicopter's flightpath. Although the helicopter operated normally after the event, the pilot chose to perform a precautionary landing to an open field. During the postflight inspection, the flight crew determined that the left sliding cabin door had separated from the helicopter. A postaccident examination did not reveal any anomalies consistent with a failure of the door assembly or airframe structure that would have led to the separation. The helicopter's Pilot's Operating Handbook stated that the helicopter could be flown up to 120 knots with an open door if it is in the "full open" position and secured by the door latch. The lack of the door latch pin allowed the door to slide forward during flight and then aerodynamic forces separated the door from the sliding track.

Verbatim NTSB analysis and probable cause from the NTSB dataset