HSI (Horizontal Situation Indicator)

HSI (Horizontal Situation Indicator) is a cockpit instrument that combines a heading indicator with a VOR/ILS course deviation indicator on a single display. It provides an intuitive top-down view of the aircraft's heading relative to the selected navigation course, eliminating the need to mentally correlate separate instruments.

Shows: aircraft heading, selected course, course deviation (CDI), glideslope deviation, TO/FROM indicator
Rotating compass card shows current heading at the top
Course pointer rotates to show the selected VOR radial or ILS localizer
Modern glass cockpits integrate HSI functions into the Primary Flight Display (PFD) or Navigation Display (ND)