An attitude indicator (AI), also known as gyro horizon or artificial horizon or attitude director indicator (ADI, when part of an Electronic flight instrument system), is an instrument used in an aircraft to inform the pilot of the orientation of the aircraft relative to Earth's horizon. It indicates pitch (fore and aft tilt) and bank (side to side tilt) and is a primary instrument for flight in instrument meteorological conditions.
Attitude indicators are also used on manned spacecraft, where they indicate the craft's yaw angle (nose left or right) as well as pitch and roll, relative to a fixed-space inertial reference frame.
The essential components of the indicator are:
"miniature airplane", horizontal lines with a dot between them representing the actual wings and nose of the aircraft.
the center horizon bar separating the two halves of the display, with the top half usually blue in color to represent sky and the bottom half usually dark to represent earth.
degree indices marking the bank angle. They run along the edge of the dial. On a typical indicator, there is a zero angle of bank index, there may be 10 and 20 degree indices, with additional indices at 30, 60 and 90 degrees.
If the symbolic aircraft dot is above the horizon line (blue background) the aircraft is nose up. If the symbolic aircraft dot is below the horizon line (brown background) the aircraft is nose down. The fact that the horizon moves up and down and turns, while the symbolic aircraft is fixed relative to the rest of the instrument panel, tends to induce confusion in trainees learning to use the instrument; a standard mental corrective provided by flight instructors is "Fly the little airplane, not the horizon."
A 45 degree bank turn is made by placing the indicator equidistant between the 30 and 60 degree marks. A 45 degree bank turn is usually referred to as a steep turn.
The pitch angle is relative to the horizon. During instrument flight, the pilot must infer the total performance by using other instruments such as the airspeed indicator, altimeter, vertical speed indicator, directional gyro, turn rate indicator, and power instruments, e.g. an engine tachometer. "Performance = Attitude + Power".
