Which instrument is designed to show an aircraft's forward velocity in knots?

The airspeed indicator is the instrument that specifically measures and displays an aircraft's forward velocity in knots. It provides essential information to the pilot regarding how fast the aircraft is moving through the air, which is critical for safe operations, including takeoff, landing, and navigation.

The airspeed indicator works by comparing the dynamic pressure of the air flowing over the aircraft with the static pressure, giving a direct reading of the speed in relation to the surrounding air. This measurement is vital because it helps determine how the aircraft will perform under different conditions, such as climb or descent rates, and helps ensure the aircraft remains within its operational limits.

In contrast, the altimeter measures altitude, the turn and slip indicator helps assess the aircraft's rate of turn and coordination, and the rate of climb indicator shows the vertical speed of the aircraft, none of which provide information regarding forward velocity in knots. Understanding this distinction is crucial for flight safety and effective aeronautical decision-making.