What happened
On November 20, 2014, a BAe Jetstream 3102, registration ES-PJA, operated by AS Avies, was conducting a scheduled commercial flight from Sveg to Stockholm/Arlanda. During the flight, the crew noticed a warning light indicating a shut valve issue on the right-side hydraulic pump. Upon investigation, the pilots discovered that hydraulic pressure from the left-side pump was also dropping.
Despite attempts to restore pressure by activating the right-side pump, the fluid loss continued. Following the aircraft's emergency checklist, the crew notified air traffic control and prepared for an emergency landing. Because the loss of pressure rendered the standard landing gear and flap deployment systems inoperable, the pilots had to use the manual hydraulic hand pump to extend the gear and set the flaps. The aircraft landed at Arlanda without further complications, though the crew had to use differential braking and engine power to steer the aircraft on the ground due to the loss of wheel steering.
The investigation
The Swedish Accident Investigation Authority (SHK) conducted a technical examination of the aircraft and the specific components involved in the leak. The investigation focused on a check valve located downstream of the right hydraulic pump, which is designed to prevent backflow.
Technical experts analyzed the fracture surface of the valve and examined the surrounding hardware. The investigation also looked into the condition of the clamps used to secure the hydraulic pipe that holds the valve in place. Additionally, the investigation reviewed the maintenance history and the operational procedures followed by the crew during the emergency.
Findings
- The loss of hydraulic pressure was caused by a leak through a fracture in the right hydraulic pump's check valve.
- The fracture in the valve was the result of high cycle fatigue caused by vibrations.
- Evidence of wear and chafing on the clamps and rubber bushings holding the hydraulic pipe suggests these components may have been deficient, potentially subjecting the pipe and valve to higher-than-normal vibration frequencies.
- The fracture occurred within a protective casing, meaning the developing crack was not visible during standard prescribed maintenance inspections.
- The crew followed all established emergency procedures, successfully using the manual extension system to ensure a safe landing.