Horizontal Situation Indicator

Encyclopedia : H : HO : HOR : Horizontal Situation Indicator

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The horizontal situation indicator (commonly called the HSI) is an aircraft instrument normally mounted below the artificial horizon in place of a conventional directional gyro which combines both the DG and the VOR display and reduces pilot workload by lessening the number of elements in his or her scan.  The HSI instrument also includes a glide slope needle so that an ILS can be flown with reference only to the six basic instruments.  Among other advantages, the HSI offers freedom from the confusion of reverse sensing.

On the HSI, your airplane appears in miniature in the center of the instrument. The VOR/ILS localizer is shown in relation to the miniature airplane. This is all on the face of the heading indicator slaved to a remote compass-a marriage of the heading indicator and VOR/ILS (with glide slope), which is frequently interconnected with an autopilot with altitude hold and the capability of following the glide slope all the way to the decision height and beyond.

On a conventional VOR indicator, left/right and to/from must be interpreted in the context of the selected course. When an HSI is tuned to a VOR station, left and right always mean left and right and TO/FROM is indicated by a simple needle pointing to the VOR. If the arrow points ahead of you, it means TO, and if it points behind you, it means FROM.

Horizontal Situation Indicator

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