Attitude Indicator :
Provides a substitute for the earth’s horizon. The attitude indicator displays scales that allow the pilot to set climb / dive angles and bank angle (Very important aspects of instrument flying).
The Attitude Indicator shows the aircraft’s position in relation to the earth’s horizon. The white semi-circle of the instrument represents the sky. The white dot at the center of the display represents the nose of the airplane in relation to the horizon and the whitel bars represent the wings of the airplane.
In straight and level flight, the nose and wings correspond to the horizon line (see figure). At the top of the indicator is a marker and ball. The ball is covered by the marker indicating level flight. Although this instrument is used at all times, it is particularly important at night and when flying in clouds in order to control the position of airplane relative to the earth. See the examples given below for details.
The attitude indicator plays a vital role in overcoming our sensory information that serves us well on the ground but provides incorrect and disorienting data at night or in the weather. The following list addresses some of the false sensations a pilot can experience from the inner ear (vestibular system) :
Action : Prolonged constant turn
Sensation : No sensation of turning
Action : Forward acceleration
Sensation : Tilting backwards (sensation of climbing)
Action : Accelerating in a turn
Sensation : Sensation of turning clockwise
Another sensory source that can provide incorrect data is the somatosensory system (commonly referred to as “seat of the pants”). On the ground, our numerous “sensors” of the somatosensory system feel the pull of gravity and tell us which way is down. However, in flight a pilot can pull “Gs” that are greater than the force of gravity (a 60 degree level turn produces 2 “Gs” or twice the force of gravity) and override this system making the pilot think that “down” is somewhere it isn’t!
Pitch Level, Shallow Left Bank :
Since the left wing is dipped below the horizon, the plane is banking to the left. Since the wing line crosses the horizon, as well, then the plane’s pitch is level. Notice the marker and ball at the top of the indicator. If the marker is to the left of the ball, then the plane is banking left.
Pitch Nose Up, Wings Level :
Since the wing line is completely above the horizon, that shows that the plane’s nose is pitched up. Since the wings are level with the horizon, that shows the plane is level.
Pitch Level, Medium Right Bank :
Since the right wing is dipped below the horizon, the plane is banking to the right. Since the wing line crosses the horizon, as well, then the plane’s pitch is level. Notice the marker and ball at the top of the indicator. Since the marker is to the right of the ball, the plane is banking to the right.
Pitch Nose Down, Shallow Left Bank :
Since the wing line is completely below the horizon, that shows that the plane’s nose is pitched down. Since the left wing is below the right wing, that shows the plane is banking to the left. Notice the ball and marker at the top of the indicator. Since the marker is to the left of the ball, but not by much, then the plane is making a shallow bank to the left.