Attitude indicator

Proposals of such devices based on gyroscopes, or spinning tops, date back to the 1740s,[5] including the work of John Serson.

[7] 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.

A symbol representing the aircraft (which is fixed in a Western instrument) rolls left or right to indicate bank angle.

[9] The heart of the AI is a gyroscope (gyro) that spins at high speed, from either an electric motor, or through the action of a stream of air pushing on rotor vanes placed along its periphery.

It may take a few minutes for the erecting mechanism to bring the gyros to a vertical upright position after the aircraft engine is first powered up.

[11] The instrument may develop small errors, in pitch or bank during extended periods of acceleration, deceleration, turns, or due to the earth curving underneath the plane on long trips.

[14][15] Attitude and Heading Reference Systems (AHRS) are able to provide three-axis information based on ring laser gyroscopes, that can be shared with multiple devices in the aircraft, such as "glass cockpit" primary flight displays (PFDs).

Rather than using a spinning gyroscope, modern AHRS use solid-state electronics, low-cost inertial sensors, rate gyros, and magnetometers.