What does a barometric altimeter rely on for altitude readings?

• A. Internal calibration systems
• B. The external air pressure around the aircraft
• C. Wind speed measurements
• D. Engine thrust factors

Answer: (B)

A barometric altimeter measures altitude based on the external air pressure surrounding the aircraft. As an aircraft ascends, the air pressure decreases, and the barometric altimeter is designed to detect this change. The altimeter uses a sealed aneroid capsule that expands or contracts with variations in external pressure. This mechanical movement is then translated into altitude readings.

Understanding this principle is critical for pilots, as accurate altitude readings are essential for safe navigation and maintaining appropriate vertical separation from other aircraft. The reliance on external air pressure is a foundational characteristic of how barometric altimeters function, distinguishing them from other potential measures, such as wind speed or internal engine characteristics. Thus, the correct choice reflects the fundamental operating principle of barometric altimetry in aviation.