What happened
On August 17, 2012, a professional pilot operating a Cirrus SR22 was conducting a cross-country flight. Upon reaching cruising altitude, the pilot attempted to implement a fuel-lean mixture procedure in accordance with the aircraft's Pilot Operating Handbook (POH) to achieve an economy cruise setting. Following the adjustment, the pilot noticed irregular engine operation. In response, the pilot transitioned the mixture to a "rich" setting, initiated a descent, and returned to the departure airport, Poznań-Ławica (EPPO). The pilot performed a normal landing without further complications.
The investigation
Following the landing, the aircraft's engine monitor data was analyzed, which initially showed no deviations from normal operating parameters. A more in-depth technical analysis, conducted in coordination with a service station in Schonhagen, Germany, revealed that the engine roughness was caused by the pilot reducing the fuel flow to the levels specified in the POH while simultaneously maintaining an disproportionately high boost pressure. The investigation established that the pilot had attempted to adjust the parameters to reach a Turbine Inlet Temperature (TIT) of 1600°F or lower. While the operator provides this temperature value as a secondary method for pilots to verify the correctness of the procedure, it is not intended to be a primary target parameter.
Findings
- The engine irregularity was caused by the pilot reducing fuel flow to the POH-recommended level while maintaining an excessively high boost pressure.
- The pilot's actions were driven by an attempt to achieve a specific Turbine Inlet Temperature (TIT) of 1600°F or less.
- The pilot's decision to return to the airport following the engine symptoms was considered a correct and appropriate precautionary measure.
- The incident was classified as a pilot technique error that did not pose a direct threat to flight safety.
Safety action
- The pilot received additional training regarding the relationship between thermodynamic parameters in engines.
- The incident was reviewed during a periodic safety meeting by the operator.