What instrument indicates the speed of the aircraft?

The airspeed indicator is the instrument specifically designed to measure the speed of the aircraft relative to the surrounding air. It provides crucial information that enables pilots to understand their speed during various phases of flight, such as takeoff, cruising, and landing. The airspeed indicator displays airspeed in knots or miles per hour and is essential for maintaining control and ensuring safe flight operations.

In aviation, understanding airspeed is vital because it affects various performance aspects of the aircraft, such as stall speed, fuel efficiency, and the ability to climb, descend, or navigate through varying weather conditions. The readings from the airspeed indicator are based on dynamic pressure from the airflow entering the pitot tube, which is a fundamental principle in aerodynamics.

In contrast, the other instruments mentioned serve different purposes. The speedometer is primarily used in road vehicles, the altimeter measures altitude based on atmospheric pressure, and the vertical speed indicator shows the rate of climb or descent but does not provide actual speed information. Each instrument plays a unique role in flight, but the airspeed indicator is singular in its function of measuring the speed of the aircraft.