What is the primary function of an aircraft's altimeter?

Answer: B — To measure altitude based on air pressure changes

The primary function of an aircraft's altimeter is to measure altitude based on air pressure changes. As an aircraft ascends or descends, the atmospheric pressure around it changes. The altimeter senses these changes in pressure and translates them into altitude readings. This mechanism is crucial for pilots to maintain a safe flying altitude, avoid collisions with terrain or other aircraft, and follow air traffic control regulations. Unlike tracking speed, calculating fuel consumption, or monitoring direction, which involve different instruments and systems, the altimeter specifically focuses on determining how high an aircraft is flying in relation to sea level or ground level. Understanding this function helps pilots utilize the altimeter effectively for safe navigation and adherence to altitude requirements during flight operations.