After installing a new fuel control unit on a turbine engine, a technician performs an engine trim run per the maintenance manual, checking engine speed against EPR or EGT at a specified reference OAT and barometric pressure. What is the primary purpose of this engine trim procedure?
- ATo adjust the clearance of compressor bleed valves for proper stall margin
- BTo calibrate the main oil pressure relief valve setting to specification
- CTo verify and adjust the fuel control unit so the engine produces its rated thrust output at a specified reference power setting without exceeding operating limits
- DTo statically and dynamically balance the compressor rotor after blade replacement
Show answer & explanationAnswer & explanation
Correct answer: C. To verify and adjust the fuel control unit so the engine produces its rated thrust output at a specified reference power setting without exceeding operating limits
Engine trimming is performed to verify that a newly installed or adjusted fuel control unit delivers the correct fuel flow so the engine develops its rated thrust (checked via EPR or EGT/N1 relationships) at a reference power lever setting, under specified ambient temperature and pressure conditions, without exceeding temperature or speed limits.
Why the other options are wrong
- A. Bleed valve clearance adjustment is a separate rigging task, not the purpose of engine trim.
- B. Oil pressure relief valve calibration is unrelated to engine trim, which concerns fuel scheduling/thrust output.
- D. Rotor balancing is a separate procedure unrelated to fuel control trimming.
Engine Trim
A maintenance procedure that verifies and adjusts a turbine engine's fuel control unit so the engine achieves its rated thrust output at a specified reference power setting under known ambient conditions.
- Performed after FCU installation, adjustment, or engine change
- Uses EPR, EGT, or N1 relationships compared to reference charts corrected for OAT/pressure
- Ensures engine meets thrust output without exceeding temperature/speed limits
Memory trick: Engine trim = fine-tuning the throttle's promise to deliver exact rated thrust