Horizontal Situation Indicator (HSI)

The Horizontal Situation Indicator (HSI) is an instrument that combines the heading indicator and course deviation indicator (CDI) into a single integrated display. It shows the aircraft’s magnetic heading, the selected course (VOR radial or localizer), and the lateral deviation from that course, all on one instrument face.

HSI vs. Conventional CDI + HI

With a conventional setup (separate HI and CDI), the pilot must mentally integrate heading with course to understand the angular relationship. The HSI does this automatically — the course pointer is overlaid on the rotating compass card, showing the angular difference between heading and course at a glance. This dramatically reduces the cognitive workload for instrument navigation.

Reading the HSI

• The lubber line at the top of the HSI shows the current magnetic heading
• The course pointer (arrow) shows the selected course (set with the course knob)
• The CDI bar shows left/right deviation from the selected course
• The TO/FROM indicator shows whether the selected course takes the aircraft toward or away from the navaid

Related Terms

See also: Heading Indicator, CDI, VOR.