What is the primary function of an altimeter in an aircraft?

The primary function of an altimeter in an aircraft is to measure the altitude by comparing atmospheric pressure. Altimeters work based on the principle that atmospheric pressure decreases as altitude increases. The device is calibrated to read altitude in feet or meters based on the standard atmospheric pressure at sea level. By measuring the ambient air pressure outside the aircraft, the altimeter can provide the pilot with an accurate reading of how high the aircraft is flying above sea level or ground level, depending on the calibration.

This function is crucial for safe flying, particularly when it comes to maintaining altitude, avoiding terrain, and complying with air traffic control instructions. Pilots rely on these readings to ensure they are at the correct altitude for their flight path and to manage their ascent and descent properly during takeoff and landing.