What happened
On 30 September 2015, a Saab 340B, registration G-LGNJ, was performing a scheduled commercial flight from Rotterdam The Hague Airport to Aberdeen International Airport. During the initial climb, the flight crew received a hydraulic caption light and an aural warning. Upon inspection, the crew noted that while emergency pressure remained normal, the main hydraulic pressure was low and fluid quantity was decreasing.
After performing troubleshooting in a nearby holding pattern, the crew decided to return to Rotterdam. During the approach and subsequent landing on runway 06, the crew attempted to use the hydraulic hand pump to increase brake accumulator pressure to facilitate taxiing. However, the pressure failed to increase, and the captain was forced to maintain braking pressure using his feet.
As the crew proceeded with the normal engine shutdown checklist on the runway, the movement of the condition lever to the start position caused the aircraft to roll forward and to the left. The aircraft eventually came to a stop in the grass on the left shoulder of the runway. An emergency evacuation was conducted, and all 15 passengers and 3 crew members were evacuated without injury.
The investigation
The investigation focused on the mechanical cause of the fluid loss and the procedural errors that led to the excursion. Investigators examined the hydraulic system, specifically the landing gear components, and reviewed the aircraft's maintenance history and the operator's abnormal checklists. The investigation also looked into the crew's use of the hydraulic hand pump and the decision-making process regarding the engine shutdown and subsequent evacuation.
Findings
- The primary cause of the hydraulic failure was a broken aluminum down lock swivel on the right-hand main landing gear, which failed due to fatigue.
- The flight crew failed to immediately execute the memory item to switch off the electric hydraulic pump following the initial failure.
- The layout of the abnormal hydraulic malfunction checklists contributed to the incident, as the crew missed specific instructions regarding alternative engine shutdown procedures during ground operations with low hydraulic pressure.
- The crew's use of the hydraulic hand pump may have inadvertently caused an overpressure, triggering relief valves and spilling limited hydraulic fluid.
- The checklist for hydraulic fluid loss lacked clear information regarding the limited capacity of the hand pump reservoir, which is limited to approximately 150 strokes.
- The captain's decision to perform an emergency evacuation deviated from the operator's established procedures, as a normal disembarkation would have been safe given the circumstances.
Safety action
Following the incident, the operator replaced all aluminum swivels in its Saab 340B fleet. Both the manufacturer and the operator are working to amend the hydraulic malfunction checklists to provide clearer, more directive instructions for ground operations and to highlight the limitations of the hand pump system.