An attitude indicator is an invaluable tool that is used to reference an aircraft’s pitch and bank against an artificial horizon. However, it is prone to error – the two most common of which are power failures and precession errors.
If your aircraft is equipped with an electrically-driven attitude indicator, it should warn you in the event of a power failure.
If equipped with a vacuum-driven attitude indicator, you may not be warned and have to deal with an instrument that is slow to erect and receives false indications instead. Vacuum attitude indicators are more susceptible to contamination and leaks that can result in inaccurate indications that reduces airflow through the instrument. They can also fail instantly, which can render the attitude indicator immediately useless.
To make sure this isn’t an issue, make sure that you regularly check the suction gauge to see that approximately 3–5 in. Hg is being provided.
Precession errors can occur during rapid turns and changes in speed. When this happens, errors in pitch attitude and bank angle can be present. While these errors may not to too great, they can easily be identified and corrected for.
During a rapid change of speed, additional g-forces can be exerted on an aircraft. This can cause the horizon line to move to an incorrect position, albeit only slightly.
During rapid acceleration, the attitude indicator will indicate a false climb. During rapid deceleration, the attitude indicator will display a greater pitch-down attitude than reality.
During either a rapid acceleration or deceleration, what you want to do is make sure that you check in on the altimeter, vertical speed indicator, and airspeed indicator – and make sure that you use the appropriate instruments to either maintain altitude in level flight or maintain airspeed in a climb or descent.
Skids, slips, and turns can also exert additional forces and result in false indications. These can be corrected by referencing the heading indicator and turn coordinator.
Another thing to watch out for is tumbling, especially with older gyros. This can occur if 100-110° of bank or 60-70° of pitch is exceeded, and cause limitations on the degrees of bank and pitch that can be displayed. It can then take anywhere between a few seconds to several minutes for things to stabilize again.
While an attitude indicator is prone to errors and may even become unusable in certain scenarios, just know that other flight instruments can be used to account for and/or correct these errors.