Why is maintaining a current altimeter setting critical?

Maintaining a current altimeter setting is critical because atmospheric pressure is not constant and can fluctuate based on weather conditions, altitude, and geographical location. Each change in atmospheric pressure affects the way an altimeter reads altitude. If an aircraft uses an outdated altimeter setting, it may not accurately reflect the current altitude relative to sea level, potentially resulting in an unsafe situation such as flying at an incorrect altitude above ground level.

By continuously updating the altimeter to the latest local setting, pilots ensure that they have a precise understanding of their aircraft’s altitude. This practice is essential for safe vertical separation from terrain and other aircraft, especially in controlled airspace and during landing and takeoff. Maintaining an accurate reading helps pilots make informed decisions, ensuring safety during flight operations.