Circumstances:
Both aircraft were parked side by side. Because the battery was low in HGW, it had to be started by hand swinging the propeller. The pilot of HGW swung the propeller while the pilot of FEU occupied the cockpit. After the engine was started, the pilot of FEU returned to his aircraft and started its engine. The pilot of HGW returned to his cockpit to reset the engine speed for warmup but he did not actually enter the cockpit. He then left the aircraft with the engine running to get a weather report. Shortly afterwards, the pilot of FEU noticed that HGW was starting to move forward and turn towards FEU. The pilot of FEU left his cockpit and tried to manoeuvre the tail of HGW to direct it away from FEU, but was not successful and the two aircraft collided, with engines running. The pilot of HGW believed that the pilot of FEU had set the park brake for the engine start. He did not check it himself before leaving the aircraft with its engine running.
