Course deviation indicator

A course deviation indicator (CDI)^[1] is an avionics instrument used in aircraft navigation to determine an aircraft's lateral position in relation to a course to or from a radio navigation beacon. If the location of the aircraft is to the left of this course, the needle deflects to the right, and vice versa.

^ FAA (2016). "16. Navigation". Pilot's Handbook of Aeronautical Knowledge (PDF). p. 23. The CDI is found in most training aircraft. It consists of an omnibearing selector (OBS) sometimes referred to as the course selector, a CDI needle (left-right needle), and a TO/ FROM indicator.

[1] FAA (2016). "16. Navigation". Pilot's Handbook of Aeronautical Knowledge (PDF). p. 23. The CDI is found in most training aircraft. It consists of an omnibearing selector (OBS) sometimes referred to as the course selector, a CDI needle (left-right needle), and a TO/ FROM indicator.

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