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Horizontal Situation Indicator (HSI)

The HSI provides a basic horizontal view of the aircraft's navigation picture. In the F-15E, it can provide navigation data to selected ground navigation facilities (TACAN or Instrument Landing System (ILS)) or to onboard navigation systems like the Inertial Navigation System (INS).

Instrument flying without an HSI requires a fair amount of mental gymnastics; for this reason, the HSI is becoming more prevalent in general aviation since it provides an excellent picture for precise navigation.

The electronic HSI in the F-15E provides a wealth of information. In the example below, the HSI provides the crew with the bearing and range to the selected TACAN (a ground based navigation instrument that transmits a signal 360 degrees from the station) is 305 degrees and 16.0 miles (the time required to fly to the TACAN is 2 minutes and 20 seconds); the bearing and distance to the point the INS is steering to is 105 degrees and 12 miles (the time required to fly to the INS steering point is 1 minute and 48 seconds).

TACAN INS
data data

Funded in part by

Used with permission From
90th Fighter Squadron
"Dicemen" Aviation

Updated: February 24, 1999