Narrative:N1002G, the second DC-9-80 series prototype took off from Yuma, AZ at 18:20 for a certification test flight to demonstrate that the plane could be landed safely with a complete failure of its hydraulic systems. The crew were to fly a low approach, go around and another approach with a full stop landing. Both approaches to be flown without hydraulic pressure. The second approach was rejected at about 800 feet agl because the warning light for "parking brakes set" was lit. The aircraft was positioned for another approach to runway 21R. The aircraft touched down at around 175 knots just past the arresting cable, 1,831 feet beyond the landing threshold of the runway. Reverse was used before touchdown of the nosegear. The aircraft yawed and ground looped and ran off the right side of the runway. After the aircraft left the pavement, the left main gear collapsed and the right main gear and the nose gear separated from the aircraft. The aircraft came to rest on its lower fuselage about 50 feet beyond the right edge. Two 50-ton cranes then tried to lift the aircraft; one of the cranes broke and fell on top of the fuselage.
PROBABLE CAUSE: "Inadequate procedures established for certification test flight, and the pilot's mismanagement of thrust following the initial loss of directional control"
Official accident investigation report