What happened
On September 14, 2016, a Bombardier DHC-8-400 operated by PLL LOT SA was positioned at Warsaw Chopin Airport (EPWA) for departure. At approximately 15:00 UTC, during the engine start-up sequence at the parking stand, the crew observed a #3 HYD PUMP warning signal.
In accordance with standard operating procedures, the crew followed the relevant checklists and subsequently shut down the engines. The Maintenance Control Center (MCC) was notified of the technical discrepancy.
The investigation
Following the occurrence, maintenance personnel conducted a thorough inspection of the aircraft's systems. The investigation focused on the electrical components associated with the hydraulic system to identify the source of the warning light.
Findings
Technical inspections revealed that the warning was caused by a short circuit within the #3 HYD PUMP electrical relay. Maintenance crews replaced the faulty relay, after which the aircraft was returned to service and the scheduled flight was completed following a delay. An Air Safety Report (ASR) was filed regarding the incident.