The Attitude Indicator (AI) works by means of a gyro mounted on a horizontal plane and depends upon the principle of rigidity in space for its operation. The horizon bar represents the true horizon and is fixed to the gyro; it remains in a horizontal plane as the airplane is pitched or banked about its lateral or longitudinal axis, indicating the attitude of the airplane relative to the true horizon. The instrument may tumble if bank limits exceed 100 to 110 degrees or pitch limits exceed 60 to 70 degrees. There could be a slight nose-up indication during a rapid acceleration and a nose-down indication during a rapid deceleration. There is also a possibility of a small bank angle and pitch error after a 180 degree turn. On rollout from a 180 degree turn, the Attitude Indicator will indicate a slight climb and turn in the opposite direction of rollout. These inherent errors are small and correct themselves within a minute or so after returning to straight-and-level flight. Pitch attitude is determined directly by the attitude indicator and indirectly by the altimeter, the vertical speed indicator (VSI), and the airspeed indicator (ASI). As a rule of thumb, for altitude errors of less than 100 feet, use a half bar width correction on the attitude indicator; for errors in excess of 100 feet, use a full bar width correction (On an EFD use a pitch change of 1 degree or 1/5 the thickness of the chevron). If the horizon bar fails to remain in the horizontal position during straight taxiing, or tips in excess of 5 degrees during taxi turns, the instrument is unreliable. There is a four step process to change attitude: 

1. Establish (adjust pitch and/or bank in conjunction with power)

2. Trim

3. Cross-Check

4. Adjust