What happened
On January 26, 2018, a Bombardier Challenger 300 was performing a flight from Vienna (LOWW) to Sofia (LBSF) with five passengers on board. At 14:10 UTC, while taxiing from the General Aviation-West platform to runway 29 via taxiways "Q" and "M", the crew observed a yellow cockpit alert indicating low hydraulic pressure (R HYD PRESS LOW).
Upon noticing the alert, the crew identified a hydraulic fluid leak originating from the right-hand hydraulic system. In response to the failure, the pilots elected to shut down the right engine and return to the parking stand. The taxiing process concluded at 14:26, and the aircraft was subsequently placed in an Aircraft on Ground (AOG) status.
The investigation
The investigation focused on the source of the pressure drop and the subsequent leak. Maintenance inspections were conducted by a Part 145 organization, Jet Aviation Vienna. The inspection revealed a leak in the vicinity of the main landing gear, specifically at the connection of the right-hand brake shutoff valve.
Technicians identified looseness in the elbow fitting nut. During the repair process, the right-hand brake shutoff valve component was replaced with a refurbished unit, and the hydraulic line was replaced with a new one. The fitting nut was tightened by one turn, and leak tests were successfully performed before the aircraft was returned to service.
Findings
- The direct cause of the incident was a mechanical failure of the elbow fitting connecting the hydraulic line to the right-hand brake shutoff valve, which resulted in the hydraulic fluid leak.
- The inspection also noted that the elbow fitting nut had become loose.