Incident Overview
A twin-engine airplane encountered a loss of control during a test flight of an experimental parachute system. The flight was conducted at 20,000 feet and 180 knots in cruise conditions. The test involved a 331-pound anthropomorphic dummy rigged to the parachute. Two crewmembers were tasked with pushing the dummy out of the cabin door, with the parachute designed to deploy via a static line secured to a floor seat track.
Previous Incident and Static Line Modification
A prior test flight had experienced control problems when a pin on the static line became entangled with the elevator hinge. In response, the static line length was reduced from 14 feet to 9 feet. As a result, during the accident flight, the shortened static line was already under tension when the dummy was positioned in the doorway.
Sequence of Events
After the dummy cleared the doorway, the static line deployed the pilot chute, which subsequently deployed the drogue chute. The drogue chute cleared the top of the left horizontal stabilizer while the dummy fell below. The dummy began oscillating and struck the empennage and lower side of the horizontal stabilizer, causing partial separation and a downward bend of the stabilizer about midspan. The dummy then became entangled on the left horizontal stabilizer.
The entanglement caused the airplane to pitch uncommanded nose-over into a negative G arc. One crewmember was thrown about the cabin, while the second crewmember restrained himself by holding onto the static line. As the main parachute deployed, the drogue chute lines separated, allowing the dummy and parachute canopies to fall away from the aircraft. Following the separation, the airplane pitched up and initiated an uncommanded roll to the right, stopping in a fully inverted attitude. The aircraft then nosed forward and began a slow roll to the left, eventually stabilizing in a wings-level attitude. The pilots regained control, returned to the airport, and landed without further incident.
Program Review Findings
A review of the parachute test program's Test Hazard Analysis indicated that the plan's cause/effect assessment and hazard mitigation actions inadequately addressed all potential "out of aircraft" hazard possibilities, including the possibility of parachute lines or the dummy becoming entangled with the horizontal stabilizer. Furthermore, no revision to the Test Hazard Analysis was made after the previous static line entanglement incident and the subsequent shortening of the static line.