What is the main purpose of the altimeter in an aircraft?

The altimeter's primary function is to measure the aircraft's altitude relative to sea level. This instrument operates based on changes in atmospheric pressure. As an aircraft ascends, the air pressure decreases; therefore, the altimeter registers a higher altitude. Conversely, as it descends and the pressure increases, the reading on the altimeter decreases. Accurate altitude readings are vital for safe aircraft operation, enabling pilots to maintain required flight levels, avoid terrain, and comply with air traffic control instructions.

While speed measurement, cabin pressure monitoring, and navigation aid are important aspects of flight, they are not the purpose of the altimeter. Each of these functions is managed by different instruments and systems within the aircraft. This delineation underscores the specific and critical role of the altimeter in assisting pilots to ensure safe and effective flight.