What happened
On May 9, 2018, an ATR-72 operating flight SRN1987 arrived at Cologne/Bonn Airport (EDDK) from Poznań (EPPO). The flight proceeded without any technical issues during the transit. After landing on runway 14L, the crew taxied the aircraft to parking stand V53 and brought the aircraft to a stop.
Approximately 25 seconds after stopping, the captain attempted to engage the propeller brake for engine number 2 into "Hotel mode." However, the "READY" indicator light for the propeller brake system failed to illuminate. Upon inspection, the crew discovered that the pressure in the blue hydraulic system had dropped to zero, while the pressure in the green hydraulic system was also steadily decreasing.
Despite multiple attempts to activate the auxiliary hydraulic pump, the pressure could not be maintained. Consequently, the captain elected to shut down the engine without engaging the propeller brake. After connecting a ground power unit (GPU), the "LO LVL" warning light for the blue hydraulic system became active.
The investigation
The investigation, conducted by the operator, focused on the sudden loss of hydraulic pressure in the aircraft's primary systems. Technical personnel inspected the hydraulic lines and identified the source of the fluid loss. The investigation established that the pressure drop was caused by a mechanical failure within the hydraulic distribution network.
Findings
- The primary cause of the incident was a ruptured hydraulic fuse housing within the blue hydraulic system.
- The failure of the fuse housing led to a total loss of pressure in the blue system and a subsequent depletion of the green system.