What happened
During the flight to its destination, a DC-9 experienced a loss of hydraulic fluid caused by a fractured rudder shutoff valve in the right-side hydraulic system. While the left-side hydraulic system maintained normal pressure and quantity during the flight, the flightcrew declared an emergency during the approach to the destination airport. After landing, the crew negated the emergency and taxied toward the gate.
Flight data recorder information revealed that the left engine, which powers the left hydraulic system, was shut down during taxi. The captain stated he did not remember shutting down the left engine and believed any such action would have occurred after clearing all runways, while the first officer was unaware the engine had been shut down. Upon reaching the gate area, the aircraft suffered a loss of steering and braking because the left hydraulic system lacked pressure and the right system had failed.
Unable to use brakes to stop, the crew requested maintenance personnel to chock the aircraft. The crew intended to keep the engines running to maintain the use of thrust reversers; however, when the aircraft began rolling forward, the reversers failed to deploy. The DC-9 subsequently collided with a company A-319 at a speed between 15.65 and 16.34 miles per hour. Evacuation of the DC-9 was completed approximately 5 minutes and 22 seconds after the impact, while the A-319 was evacuated approximately 13 minutes and 8 seconds after the collision.
The investigation
Investigators examined the hydraulic systems and found no anomalies in the left system. The right hydraulic system examination revealed a fractured rudder shutoff valve showing features consistent with fatigue. Following this accident, the aircraft manufacturer issued a service letter regarding the replacement of the rudder shutoff valve due to reliability concerns.