What function does the altimeter serve in IFR flying?

The altimeter serves a critical function in IFR flying by indicating the aircraft's altitude above a specific pressure setting, typically set to the standard atmospheric pressure of 29.92 inches of mercury or the local altimeter setting based on atmospheric conditions. This altitude information is crucial for maintaining safe vertical separation from terrain and other aircraft, especially in the constrained environments often encountered during instrument flight.

In IFR operations, pilots rely on accurate altitude readings to ensure compliance with air traffic control instructions and to avoid obstacles. The altimeter works by measuring the atmospheric pressure surrounding the aircraft; as altitude increases, atmospheric pressure decreases. By calibrating this pressure reading against a predetermined reference, the altimeter provides a reliable measurement of the aircraft's vertical position. This function is vital for navigation and safety in the instrument flying environment.