What principle does an altimeter rely on to display altitude?

• A. Static pressure
• B. Dynamic pressure
• C. Temperature
• D. GPS altitude

Answer: (A)

An altimeter measures altitude by sensing static air pressure. As you rise, the ambient static pressure drops, and that change causes an airtight, flexible chamber (aneroid) inside the instrument to expand or contract. The mechanical linkage translates that movement into a pointer on a dial. The display is calibrated to show altitude when the local sea-level pressure is set through the altimeter setting (Kollsman window), so the reading reflects height above the reference level. Dynamic pressure is used for airspeed, not altitude, and while temperature can affect the actual pressure–altitude relationship, the fundamental principle remains static pressure. GPS altitude is a separate method and not the mechanism a traditional altimeter uses.