Which instrument is essential for maintaining level flight?

The artificial horizon, also known as the attitude indicator, is essential for maintaining level flight because it provides a visual representation of the aircraft's orientation relative to the horizon. This instrument displays whether the wings are level and the aircraft is in straight and level flight or if the aircraft is climbing, descending, or turning.

In level flight, maintaining a constant altitude requires precise control of the aircraft's pitch attitude. The artificial horizon allows pilots to quickly assess the aircraft's current attitude, making it possible to make timely corrections as needed. By ensuring that the wings remain level and the aircraft maintains the desired pitch, pilots can effectively achieve and sustain level flight.

While other instruments like the altimeter, airspeed indicator, and heading indicator provide important information, they primarily assist in determining altitude, airspeed, and course direction. They may not directly reflect the aircraft's attitude relative to the horizon, which is crucial for maintaining level flight.