FAA Powerplant Written Practice Test

What device controls turbocharger speed and output without pilot intervention up to critical altitude?

1. Variable nozzle actuator

2. Absolute pressure controller

3. Electronic control unit

4. Throttle body

The correct answer is: Absolute pressure controller

The correct answer is that the device which controls turbocharger speed and output without pilot intervention up to critical altitude is the absolute pressure controller. This device plays a vital role in managing the turbocharger by automatically adjusting the flow of exhaust gases to the turbine based on the aircraft's altitude and engine parameters. As altitude increases, manifold pressure decreases, and the absolute pressure controller helps maintain the desired boost level by regulating turbocharger performance. This ensures optimal engine power and efficiency without requiring manual adjustments by the pilot during flight, allowing for a steady output and improved performance at higher altitudes. In contrast, the variable nozzle actuator is responsible for adjusting the geometry of the turbocharger's nozzle to optimize efficiency but does not directly manage speed or output without pilot involvement. The electronic control unit, typically involved in broader engine management and control strategies, also oversees multiple systems beyond just the turbocharger, making it less specific to the task described in the question. Lastly, the throttle body is primarily used for regulating air intake into the engine, not directly controlling turbocharger performance.