At 10:30 PDT, a Beech 65-90 became entangled with a deploying parachute. The accident sequence was filmed by several video cameras from different angles and perspectives. While stabilized at 20,000 feet msl and 180 knots, two crewmembers in the back of the aircraft ejected a 331-pound dummy rigged with a main and reserve parachute. As the dummy cleared the doorway, the pilot chute from the main parachute deployed, immediately followed by the deployment of the drogue chute. The drogue chute traveled above the left horizontal stabilizer while the dummy fell below. The dummy became entangled on the left horizontal stabilizer and the aircraft made an uncommanded noseover into a negative G arc. Then the main chute deployed and the drogue chute lines separated. The dummy fell freely from the aircraft as the main canopy opened. As the dummy fell away, the aircraft pitched up and began an uncommanded roll to the right, stopping in a fully inverted attitude. The pilot was able to recover and returned to the airport and landed without further incident. During the accident sequence, one crewmember who had crouched behind the dummy for the test deployment was thrown about the cabin and received serious injuries. The other crewmember in the back of the airplane held onto the static line and was uninjured.