What happened
On May 5, 2017, at approximately 14:50 UTC, the crew of a Bombardier DHC-8-402 was performing a pre-flight inspection at Ljubljana Airport (LJU) when they detected traces of hydraulic fluid leaking from the number two engine nacelle. Following an engine run test, the crew observed an increase in the leakage, prompting the cancellation of the scheduled flight.
Because the aircraft's operator did not have contracted maintenance services available at Ljubljana, a technical team was dispatched from Warsaw Chopin Airport (EPWA) to address the issue. Upon arrival, maintenance personnel inspected the engine nacelle and found that the hydraulic overflow bottles (ECO) were overfilled and identified two loose hydraulic line connections. The connections were tightened in accordance with the Aircraft Maintenance Manual (AMM), and the overflow bottles were cleaned. After passing a subsequent leak test, the aircraft was cleared to ferry to its home base.
However, upon arrival at EPWA, maintenance crews detected traces of hydraulic fluid leaking once again. To locate the source of the leak, technicians were required to remove the engine exhaust pipe. This inspection revealed a chafed hydraulic line located between the hydraulic fluid reservoir and hydraulic manifold number 2.
The investigation
The investigation focused on the sequence of maintenance actions and the physical condition of the hydraulic system components. The technical team examined the engine nacelle, the hydraulic line connections, and the area between the reservoir and the manifold to identify the source of the fluid loss.