FAA Powerplant Written Practice Test

What conditions might require re-trimming of a turbofan engine?

1. Insufficient airspeed during takeoff

2. Replacement of fuel control or engine not developing maximum thrust

3. Poor fuel quality during operation

4. Engine operating outside design temperature

The correct answer is: Replacement of fuel control or engine not developing maximum thrust

Re-trimming of a turbofan engine may become necessary in the context of maintenance and performance adjustments, particularly when there has been a replacement of the fuel control system or if the engine is not developing maximum thrust. When a fuel control unit is replaced, it can introduce variations in fuel flow, which may affect the engine's performance characteristics. The engine's fuel delivery system must be recalibrated or re-trimmed to ensure that under all operating conditions, appropriate fuel is delivered for optimal engine performance, efficiency, and to meet the thrust demands during various phases of flight. This is critical, especially for achieving the required maximum thrust during critical operations like takeoff. Additionally, if the engine is not developing maximum thrust, it's indicative that the engine may not be operating optimally. In either scenario, re-trimming would help to recalibrate the engine parameters to correct or restore proper performance levels. Other conditions such as insufficient airspeed during takeoff, poor fuel quality, or operating outside design temperature can lead to various performance issues but do not directly necessitate a re-trimming of the fuel control systems or adjustments that are specifically associated with the fuel control changes needed for engine performance optimization.