Situational Awareness
Aircraft Equipment Problem Critical
General None Reported / Taken
Aircraft; Human Factors
During climb out at approximately 1;500 ft. AGL the door warning annunciator actuated. No obvious door abnormalities were observed by the flight crew and the flight continued to ZZZ. During descent into ZZZ the top clam shell hatch on the main cabin door opened. PIC was entering a left downwind to Runway XX when the door opened. Passengers were instructed to remain calm and do not touch the door. PIC [advised ATC] to ensure priority to the runway. Landed without incident.
Pilot reported that a malfunction caused a door to open in flight.