Case Description
Issue:
The Utility Hydraulic System pressure fluctuates between 2800 and 3200 PSI during flight control inputs. The low-pressure warning light flickers intermittently during flap retraction.
Investigation:
1. Checked fluid quantity in the reservoir; found normal.
2. Inspected the engine-driven pumps (EDP) for case drain flow; No. 1 EDP indicated high case drain flow.
3. Replaced the system filter; found metallic particles in the element.
4. Performed accumulator pre-charge check; found low nitrogen charge (800 PSI instead of 1500 PSI).
Root Cause:
The accumulator pre-charge was low, causing the system to lose damping capability during high-demand operations (flap retraction). Additionally, the No. 1 Engine Driven Pump was showing signs of internal wear (metallic particles), contributing to the instability.
Lessons Learned
- Don't ignore "minor" fluctuations; they are often precursors to pump failure.
- Accumulator pre-charge checks should be part of the initial troubleshooting for any pressure fluctuation issue.
- Always inspect filters for contamination when hydraulic components are suspected of failure.