The attitude indicator (AI), formerly known as the gyro horizon or artificial horizon, is a flight instrument that informs the pilot of the aircraft orientation relative to Earth’s horizon, and gives an immediate indication of the smallest orientation change. The miniature aircraft and horizon bar mimic the relationship of the aircraft relative to the actual horizon. It is a primary instrument for flight in instrument meteorological conditions.
The essential components of the AI include a symbolic miniature aircraft mounted so that it appears to be flying relative to the horizon. An adjustment knob, to account for the pilot’s line of vision, moves the aircraft up and down to align it against the horizon bar. The top half of the instrument is blue to represent the sky, while the bottom half is brown to represent the ground. The bank index at the top shows the aircraft angle of bank. Reference lines in the middle indicate the degree of pitch, up or down, relative to the horizon.