FAA Powerplant Written Practice Test

The primary purpose of the tachometer on an axial-compressor turbine engine is to monitor engine RPM during starting. The tachometer provides critical information about the rotational speed of the engine, which is essential for ensuring safe operation and preventing potential damage during the startup phase. During engine startup, monitoring RPM helps the operator assess whether the engine is accelerating as expected and reaching the desired operating conditions.

This monitoring is crucial because abnormal RPM readings can indicate issues such as compressor stall or a malfunction within the engine, prompting corrective actions before further operation. The tachometer plays a vital role in maintaining engine health and ensuring reliability, especially during the critical phases of engine operation, such as starting.

The other choices, such as measuring fuel efficiency, indicating fuel flow rate, or providing exhaust gas temperature readings, relate to different aspects of the engine's performance and operation but do not centralize on the specific function of monitoring RPM during the starting of the engine.