What operating parameter does a tachometer indicate?

A tachometer is an instrument that measures the rotational speed of an engine's crankshaft or a turbine rotor. It provides vital information about how fast the engine is running, typically displayed in revolutions per minute (RPM). This information is crucial for pilots and mechanics to ensure that the engine is operating within its designed parameters, avoiding over-revving which can lead to engine damage.

Understanding engine RPM is essential for optimizing performance, fuel efficiency, and engine longevity. In contrast, the other options relate to different parameters: engine temperature monitors the heat level of the engine, fuel pressure indicates the pressure of the fuel system, and airspeed measures how fast the aircraft is traveling through the air. Each of these is important for safe and efficient flight operation, but the tachometer specifically focuses on the engine's rotational speed.