Incident Overview
During approach, a fire erupted in the wheel well of a 22-year-old airplane. The fire burned through hydraulic lines, rendering the A, B, and standby hydraulic systems inoperative. The flight crew successfully landed the airplane using the emergency manual reversion flight control system. However, the airplane was unable to stop on the runway due to previous failures of check valves in the backup hydraulic accumulator pressure systems for the #2 thrust reverser and the inboard pair of wheel brakes. During the two-minute rollout, the airplane traversed approximately 14,000 feet, overran the runway end, and collided with a concrete structure, which collapsed the nose gear.
Maintenance History
The airplane had recently undergone a C check. During this maintenance, the operator's mechanics failed to observe and repair an electric wire that had been chafing against a hydraulic line. On the accident flight, the energized wire arced, punctured the hydraulic line, and ignited the escaping hydraulic fluid. Additionally, the hydraulic check valves had failed earlier due to mechanical wear.
Probable Cause
The probable cause, as determined by the official investigation, was the failure of the operator's maintenance personnel to detect an electrical wire which had chafed against a hydraulic line and which eventually arced, causing a leak in the hydraulic line and subsequent fire and hydraulic system failure. In addition, previous wear of check valves in the backup hydraulic systems prevented the airplane from stopping on the runway. A contributing factor was the airplane manufacturer's inadequate guidance for maintaining the hydraulic components.