What is the purpose of an altimeter in an aircraft?

The purpose of an altimeter in an aircraft is to measure the aircraft's altitude by comparing static air pressure. An altimeter functions by detecting the atmospheric pressure outside the aircraft and translating this into an altitude reading. As an aircraft ascends, the surrounding air pressure decreases. The altimeter responds to this change, allowing pilots to determine how high they are flying above sea level or above the ground.

The use of static air pressure is essential for accurate altitude readings because the pressure changes correspond to changes in elevation. This tool is crucial during flight operations, particularly for maintaining safe separation from terrain and other aircraft. Understanding how high an aircraft is flying enables effective navigation and adherence to altitude regulations.

The other options do not accurately describe the primary function of an altimeter. For instance, measuring ground speed and wind direction pertains to airspeed indicators and other navigation tools, while monitoring fuel levels is the domain of fuel gauges. Lastly, cabin temperature is related to environmental controls and systems onboard, rather than altitude measurement.