Incident Overview
On 26 January 2018, a Bombardier Challenger 300 aircraft operated a flight from Vienna (LOWW) to Sofia (LBSF) with five passengers and a flight crew comprising an ATPL(A) pilot, for a total of eight occupants. At 14:10 UTC, the crew received clearance to taxi from the General Aviation-West apron to runway 29 via taxiways Q and M. During taxi on taxiway M, a yellow caution message "R HYD PRESS LOW" appeared, indicating low pressure in the right hydraulic system. The pilots subsequently identified a hydraulic fluid leak from the right hydraulic system. They decided to shut down the right engine and return to the parking stand, completing the taxi at 14:26. The aircraft was declared AOG (Aircraft on Ground).
Findings
Post-incident inspection was conducted by a Part 145 maintenance organization, Jet Aviation Vienna. The examination revealed a hydraulic fluid leak in the area of the main landing gear (MLG), specifically at the connection of the right-hand (R/H) Brake Shutoff Valve. Loose torque was found on the nut of the angled connector (króćca kątowego), which was subsequently tightened by one full turn using a wrench. The R/H Brake Shutoff Valve was replaced with a refurbished unit, and the hydraulic hose was replaced with a new one. A leak test was performed, and the aircraft was returned to service.
Operator Recommendations
The operator issued several safety recommendations in response to the incident:
- Inform Jet Aviation Vienna of the findings.
- Inform the manufacturer of the findings.
- After any maintenance involving the R/H Brake Shutoff Valve, apply a red marking to the top fitting and threads to allow visual verification of proper torque.
- Inform operator personnel, including mechanics, CAM engineers, pilots, and relevant managers, of the event and recommendations.
Probable Cause
The direct cause of the incident was mechanical damage to the angled connector joining the hydraulic hose to the R/H Brake Shutoff Valve, resulting in hydraulic fluid leakage.