What does a Barometric Altimeter do?

• A. Indicates altitude above ground level using radio echoes
• B. Determines heading from magnetic north
• C. Measures aircraft speed via pitot tube
• D. Uses pitot-static pressure to indicate altitude above sea level

Answer: (D)

The main idea is that a barometric altimeter converts ambient atmospheric pressure into an altitude reading. It uses the static pressure from the pitot-static system and, with the current sea-level pressure setting, translates that pressure into altitude above mean sea level. In practice, as you climb, the surrounding air pressure drops, and the instrument’s calibrated scale shows higher altitude when the altimeter setting is adjusted to the local sea-level pressure.

This instrument doesn’t measure height above the ground (that’s what a radar or GPS altitude does), it doesn’t indicate direction or heading (that’s a compass), and it isn’t measuring speed (that’s the airspeed indicator using the pitot tube). The key point is static pressure, not dynamic pressure, is what the altimeter relies on to display altitude above sea level.