Which of the following components is not part of an aircraft instrument system?

In an aircraft instrument system, the components are specifically designed to provide critical information to the pilot regarding flight, engine performance, and navigation. Flight instruments include items like altimeters, airspeed indicators, and attitude indicators, which aid in flying the aircraft safely. Engine instruments monitor the aircraft's powerplant, tracking parameters such as temperature, oil pressure, and RPM, which are vital for ensuring the engine operates within its safe limits.

Navigation instruments are essential for determining the aircraft's position and guiding it along its flight path. They include devices like GPS, VOR systems, and autopilot systems that assist in navigation.

Hydraulic instruments, however, are not typically categorized as part of the aircraft instrument system. While the hydraulic systems play a crucial role in operating flight control surfaces, landing gear, and braking systems, they do not provide direct information to the pilot about flight status or navigation. Instead, they are part of the broader systems that support flight operations. Therefore, hydraulic instruments are considered separate from the main instrument categories directly related to piloting and situational awareness.