artificial horizon
An instrument that displays the pitch and roll of an aircraft in flight by comparing its attitude to a gyroscopically-maintained indication of the flat horizon line.
artificial horizon: the gyro that shows you which way is up
An artificial horizon is an attitude indicator that tells a pilot the aircraft's pitch and roll relative to the actual horizon, even when the real horizon is invisible. It does this by maintaining a gyroscopic reference to true vertical, then displaying the aircraft's orientation against a miniature horizon line on an instrument face. The pilot sees a small aircraft symbol fixed at the center of the dial, with a moving horizon bar behind it; when the real aircraft pitches up, the horizon bar appears to drop on the instrument, and when it banks, the bar tilts to show the bank angle.
The core mechanism is a rapidly spinning gyroscope, typically electric-driven, that resists changes in its plane of rotation. Early artificial horizons used mechanical gyros mounted in gimbals that could precess freely in pitch and roll axes. Modern variants use laser ring gyros or fiber-optic gyros in glass cockpits, which have no moving parts and drift much less over time. The display itself has evolved from electromechanical needles and cards to LCD screens in modern aircraft, but the underlying principle remains: use a stable spinning reference to maintain a virtual horizon when clouds, darkness, or disorientation make the real one useless.
In maintenance, the key concern is precession, the slow drift of the gyro's reference plane over time. Mechanical gyros can drift several degrees per hour and require periodic realignment before flight. Electric gyros in certified aircraft are designed to keep drift below 2 to 3 degrees per hour, but they still need regular erection and calibration. On the ground, a mechanic will spin up the gyro and allow it time to settle before the pilot can trust the display for instrument flight. Any vibration, temperature shock, or mechanical wear accelerates drift and makes the instrument unreliable.
The artificial horizon is mandatory for instrument flight rules (IFR) operations; it is the primary reference for attitude control when visual reference is lost. A failed or drifting artificial horizon is one of the most dangerous instrument failures because pilots depend on it completely in cloud or poor visibility. Backup systems include standby attitude indicators powered by different sources, and on modern glass cockpits, redundant air data computers that cross-check pitch and roll against inertial measurement units.
The term "artificial" distinguishes it from the actual horizon line a pilot sees by looking out the window. The word "horizon" refers to the fact that gravity defines what is level; a gyro alone does not care about gravity, but the artificial horizon gyro is erected, meaning it is mechanically rigged so that gravity keeps it aligned to true vertical during level flight. This erection mechanism is what makes the gyro useful; without it, the gyro would wander in any direction and be worthless for flying straight and level.