Horizontal situation indicator

Illustration of the face of a horizontal situation indicator showing the key elements of the display

The horizontal situation indicator (commonly called the HSI) is an aircraft flight instrument normally mounted below the artificial horizon in place of a conventional heading indicator. It combines a heading indicator with a VHF omnidirectional range-instrument landing system (VOR-ILS) display.^[1] This reduces pilot workload by lessening the number of elements in the pilot's instrument scan to the six basic flight instruments. Among other advantages, the HSI offers freedom from the confusion of reverse sensing on an instrument landing system localizer back course approach. As long as the needle is set to the localizer front course, the instrument will indicate whether to fly left or right, in either direction of travel.

On the HSI, the aircraft is represented by a schematic figure in the centre of the instrument – the VOR-ILS display is shown in relation to this figure. The heading indicator is usually slaved to a remote compass and the HSI is frequently interconnected with an autopilot capable of following the heading select bug and of executing an ILS approach by following the localizer and glide slope.^[1]

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 triangular arrowhead pointing to the VOR. If the arrowhead points to the same side as the course selector arrow, it means TO, and if it points behind to the side opposite the course selector, it means FROM. The HSI illustrated here is a type designed for smaller airplanes and is the size of a standard 3 ¼-inch instrument. Airline and jet aircraft HSIs are larger and may include more display elements.

The most modern HSI displays are electronic and often integrated with electronic flight instrument systems into so-called "glass cockpit" systems.

Notes

1 2 Instrument Flying Handbook 2012 (FAA-H-8083-15B). United States Department of Transportation, Federal Aviation Administration, Airman Testing Standards Branch. 2012. pp. 5–23, 7–38.

Flight instruments

Pitot-static	Altimeter Airspeed indicator Machmeter Variometer

Gyroscopic	Attitude indicator Heading indicator Horizontal situation indicator Turn and slip indicator Turn coordinator Turn indicator

Navigational	Course deviation indicator Horizontal situation indicator Inertial navigation system Magnetic compass Satellite navigation SIGI

Related topics	Air data inertial reference unit EFIS Glass cockpit Primary flight display V speeds Yaw string

Aircraft components and systems

Airframe structure	Aft pressure bulkhead Cabane strut Canopy Cruciform tail Dope Empennage Fabric covering Fairing Flying wires Former Fuselage Hardpoint Interplane strut Jury strut Leading edge Lift strut Longeron Nacelle Rib Ring tail Spar Stabilizer Stressed skin Strut T-tail Tailplane Trailing edge Triple tail Twin tail Vertical stabilizer V-tail Y-tail Wing root Wing tip Wingbox

Flight controls	Aileron Airbrake Artificial feel Autopilot Canard Centre stick Deceleron Dive brake Electro-hydraulic actuator Elevator Elevon Flaperon Flight control modes Fly-by-wire Gust lock Rudder Servo tab Side-stick Spoiler Spoileron Stabilator Stick pusher Stick shaker Trim tab Wing warping Yaw damper Yoke

Aerodynamic and high-lift devices	Active Aeroelastic Wing Adaptive compliant wing Blown flap Channel wing Dog-tooth Droop Flap Gouge flap Gurney flap Krueger flap Leading edge cuff LEX Slats Slot Stall strips Strake Variable-sweep wing Vortex generator Vortilon Wing fence Winglet

Avionic and flight instrument systems	ACAS Air data computer Airspeed indicator Altimeter Annunciator panel Attitude indicator Compass Course deviation indicator EFIS EICAS Flight data recorder Flight management system Glass cockpit GPS Heading indicator Horizontal situation indicator INS Pitot-static system Radar altimeter TCAS Transponder Turn and slip indicator Vertical Speed Indicator Yaw string

Propulsion controls, devices and fuel systems	Autothrottle Drop tank FADEC Fuel tank Gascolator Inlet cone Intake ramp NACA cowling Self-sealing fuel tank Splitter plate Throttle Thrust lever Thrust reversal Townend ring Wet wing

Landing and arresting gear	Arrestor hook Autobrake Conventional landing gear Drogue parachute Landing gear Landing gear extender Oleo strut Tricycle landing gear Tundra tire

Escape systems	Ejection seat Escape crew capsule

Other systems	Aircraft lavatory Auxiliary power unit Bleed air system Deicing boot Emergency oxygen system Entertainment system Environmental control system Hydraulic system Ice protection system Landing lights Navigation light Passenger service unit Ram air turbine Weeping wing

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Horizontal situation indicator

See also

Notes