Engine Trend Shift After a Compressor Wash
A B1.1 engineer supervises a compressor wash on a turbofan engine during a line check. Before the wash, the engine trend monitoring showed exhaust gas temperature (EGT) margin of 18 °C above the red line at takeoff. After the wash and a test run, the EGT margin is 9 °C, a drop of 9 °C, and the fuel flow at the same thrust has increased by 1.5%. The wash used the approved procedure and the correct fluid. The engineer also notes the engine oil consumption has risen from 0.2 to 0.35 litres per hour over the last 50 hours. The aircraft is due for a borescope at the next A-check in 120 hours. The operator asks whether the aircraft can continue to the next A-check without further action.
1. Interpret the trend data and decide whether continued operation to the next A-check is justified.
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A compressor wash normally improves EGT margin by removing fouling, so a 9 °C degradation after the wash is the opposite of the expected result and suggests the wash did not restore performance or that another factor is present. The 1.5% fuel flow increase at the same thrust and the rising oil consumption point to a real deterioration, possibly blade tip clearance, seal wear, or hot-section distress, rather than fouling. The remaining 9 °C margin is thin, and the trend is moving the wrong way. Continuing 120 hours without action is not clearly justified. The engineer should review the trend over several flights to confirm the direction, compare against the engine's trend baseline, and consider an earlier borescope, particularly of the hot section and the compressor. The oil consumption rise should be investigated for leaks or seal degradation.
2. Explain what further data the engineer should gather before making a release recommendation.
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The engineer should obtain the full trend history, not just the two points, to see whether the change is a step or a slope, and should confirm the test-run conditions matched the baseline (thrust setting, bleed configuration, ambient temperature correction). A step change after the wash suggests a wash-related effect such as residual fluid or a disturbed sensor; a continuing slope suggests wear. The engineer should check the oil system for external leaks, sample the oil for metal content, and review the last borescope findings. Comparing EGT margin against the fleet average for the same engine type and thrust rating gives context. Only with that evidence can the engineer recommend either continued operation with a shortened inspection interval or immediate corrective action; the decision should be recorded with the data that supports it.