CDI (Course Deviation Indicator)

CDI (Course Deviation Indicator) is the needle or bar on a VOR, ILS, or GPS navigation display that shows how far the aircraft is displaced laterally from the selected course. When the needle is centered, the aircraft is on course.

• Full-scale deflection on VOR: 10° off course (~1 NM per 6 NM from the station)
• Full-scale deflection on ILS localizer: 2.5° off course
• Full-scale on GPS: varies (0.3 NM for approach, 1.0 NM for terminal, 2.0 NM for en-route)
• Needle left = course is to the left; fly left to intercept (with correct OBS setting)
• Reverse sensing occurs when flying away from a VOR on the selected radial