What is the purpose of an aircraft’s altimeter?

The primary function of an aircraft’s altimeter is to measure altitude above sea level. It does this by detecting changes in air pressure as the aircraft climbs or descends. The altimeter is calibrated to the standard atmospheric pressure at sea level, allowing it to provide a relative altitude reading. When the aircraft ascends, the atmospheric pressure decreases, and the altimeter needle rises to indicate a greater altitude. Conversely, as the aircraft descends and air pressure increases, the altimeter needle decreases, reflecting a reduced altitude.

Understanding the correct altitude is crucial for safe aircraft operation, as it helps pilots maintain safe separation from terrain and other aircraft. This is particularly important in controlled airspace and during approaches to airports, where specific altitude levels must be adhered to for safety reasons. The altimeter allows pilots to reference their altitude in relation to sea level, which is a universally recognized standard.