Ramp agent reported uncommanded aircraft movement when preparing to move the aircraft from a hangar area; with the tug attached and the tug parking brake set. The aircraft began moving when the aircraft brake was released; and the loading stairs struck the aircraft door with no injuries.

Narrative

Aircraft door damaged from rolling into stairs when aircraft parking brakes were released.My observer and I were assigned to move Aircraft X from Location A at around XA:10. We approached the Aircraft and observer installed bypass pin and removed nose chocks. He went to do his walk around and I went to capture the aircraft with the Supertug. We then positioned the stairs to door 1 left. I told him to he was cleared to release brakes when he's ready. I started my walk around and removed the front left main chock and placed onto the chock dolly. As I was attempting to loosen the right front main chock I heard the brakes release and the aircraft started rolling forward and the aircraft door struck the stairs. I proceeded to run into the Tug to apply the brakes. I doubled check to confirm parking brakes were set in the Tug and it was set but did not hold. The chock I was loosening turned and went between the right main tires as I was running towards the tug. I was trained by OJT trainers from other stations that it was okay to remove one side of chocks from the main landing gear tires as long as the aircraft nose wheel has been captured by the Supertug and parking brake is set.