What is the function of the altimeter in flight?

The function of the altimeter in flight is to measure altitude relative to sea level. This instrument is critical for pilots as it provides essential data regarding the aircraft's height above a standard reference point, which is sea level in this case. The altimeter works by measuring atmospheric pressure; as an aircraft climbs, the pressure decreases, and the altimeter translates this change into an altitude reading.

Understanding altitude is vital for ensuring safe flight operations, especially when navigating through airspace where different flight levels are established. Knowing the aircraft's altitude helps pilots avoid obstacles, comply with air traffic control instructions, and ensure safe separation from other aircraft.