Which of the following is required in the minimum instrumentation for powered aircraft?

The minimum instrumentation required for powered aircraft includes specific gauges and indicators that ensure safe operation and compliance with aviation regulations. One of these essential instruments is the oil temperature gauge for engines that exceed 250 horsepower.

This requirement is critical because monitoring oil temperature helps ensure that the engine operates within safe limits. Overheating can lead to engine failure, which poses significant risks during flight. Therefore, it is essential for pilots to have access to real-time information about engine temperatures to make informed decisions regarding power settings and monitor the overall health of the engine during flight operations.

The other options listed may be useful in certain circumstances or for specific types of aircraft, but they do not constitute the minimum required instrumentation for powered aircraft in general. For example, a magnetometer may be used in navigation systems, an air pressure sensor is often part of advanced avionics or altimeter systems, and light indicators, while helpful for signaling various states of aircraft systems, do not fulfill the same critical role as an oil temperature gauge for larger engines.