What is the primary function of an altimeter in an aircraft?

The primary function of an altimeter in an aircraft is to indicate altitude above sea level. This is crucial for ensuring that the pilot maintains safe and appropriate altitude levels during flight. Altimeters work by measuring the atmospheric pressure and converting that pressure into an altitude reading. As the aircraft ascends or descends, the changes in atmospheric pressure are reflected on the altimeter, providing real-time data about the aircraft's altitude.

Measuring altitude is vital for collision avoidance, adherence to air traffic control regulations, and for navigation. Knowledge of the aircraft's altitude is essential during takeoff, landing, and throughout the flight to ensure flight safety. An accurate altitude reading allows pilots to make necessary adjustments to maintain an optimal flight profile.

In contrast, the other options involve functions that are not provided by an altimeter. For instance, measuring aircraft speed is the role of a pitot static system, assessing fuel levels is managed by fuel gauges, and the angle of descent is monitored using an inclinometer or vertical speed indicator, neither of which falls under the capabilities of an altimeter.