Horizontal Situation Indicator
HSI is the acronym for Horizontal Situation Indicator. Sometimes it is also called Pictorial Navigation Indicator. It combines a standard Directional Gyro (DG) and Course Deviation Indicator (CDI) into one single instrument and reduces the pilots workload by displaying the aircraft's heading and position relative to a desired course in a compact manner.
The well known drift of a standard Directional Gyro is usually compensated by the use of a slaved gyro system that constantly corrects the heading indication.
The purpose of this document is to briefly describe the indicators and the usage of a HSI instrument.