Horizontal Situation Indicator
Encyclopedia
The horizontal situation indicator (commonly called the HSI) is an aircraft
instrument normally mounted below the artificial horizon
in place of a conventional heading indicator
. It combines a heading indicator with a VOR
/ILS
display, reducing 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 a localizer backcourse approach. On a front course approach, the HSI needle is set to the inbound track; on a back course approach, the HSI needle is set to the outbound rather than the inbound track, causing needle deflection that mimics a front course approach instead of displaying the normal reverse sensing.
The HSI is also used on spacecraft
like the Space Shuttle
.
On the HSI, the airplane is represented by a schematic figure in the center of the instrument - the VOR
/ILS
display is shown in relation to this figure. The heading indicator is slaved to a remote compass, and the HSI is frequently interconnected with an autopilot
capable of executing an approach by following the localizer and glide slope.
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.
Aircraft
An aircraft is a vehicle that is able to fly by gaining support from the air, or, in general, the atmosphere of a planet. An aircraft counters the force of gravity by using either static lift or by using the dynamic lift of an airfoil, or in a few cases the downward thrust from jet engines.Although...
instrument normally mounted below the artificial horizon
Attitude indicator
An attitude indicator , also known as gyro horizon or artificial horizon, is an instrument used in an aircraft to inform the pilot of the orientation of the aircraft relative to earth. It indicates pitch and bank or roll and is a primary instrument for flight in instrument meteorological conditions...
in place of a conventional heading indicator
Heading indicator
The heading indicator is a flight instrument used in an aircraft to inform the pilot of the aircraft's heading. It is sometimes referred to by its older names, the directional gyro or DG, and also direction indicator or DI.- Use :The primary means of establishing the heading in most small...
. It combines a heading indicator with a VOR
VHF omnidirectional range
VOR, short for VHF omnidirectional radio range, is a type of radio navigation system for aircraft. A VOR ground station broadcasts a VHF radio composite signal including the station's identifier, voice , and navigation signal. The identifier is typically a two- or three-letter string in Morse code...
/ILS
Instrument Landing System
An instrument landing system is a ground-based instrument approach system that provides precision guidance to an aircraft approaching and landing on a runway, using a combination of radio signals and, in many cases, high-intensity lighting arrays to enable a safe landing during instrument...
display, reducing pilot workload by lessening the number of elements in the pilot's instrument scan to the six basic flight instruments
Flight instruments
Flight instruments are the instruments in the cockpit of an aircraft that provide the pilot with information about the flight situation of that aircraft, such as height, speed and altitude...
. Among other advantages, the HSI offers freedom from the confusion of reverse sensing on a localizer backcourse approach. On a front course approach, the HSI needle is set to the inbound track; on a back course approach, the HSI needle is set to the outbound rather than the inbound track, causing needle deflection that mimics a front course approach instead of displaying the normal reverse sensing.
The HSI is also used on spacecraft
Spacecraft
A spacecraft or spaceship is a craft or machine designed for spaceflight. Spacecraft are used for a variety of purposes, including communications, earth observation, meteorology, navigation, planetary exploration and transportation of humans and cargo....
like the Space Shuttle
Space Shuttle
The Space Shuttle was a manned orbital rocket and spacecraft system operated by NASA on 135 missions from 1981 to 2011. The system combined rocket launch, orbital spacecraft, and re-entry spaceplane with modular add-ons...
.
On the HSI, the airplane is represented by a schematic figure in the center of the instrument - the VOR
VHF omnidirectional range
VOR, short for VHF omnidirectional radio range, is a type of radio navigation system for aircraft. A VOR ground station broadcasts a VHF radio composite signal including the station's identifier, voice , and navigation signal. The identifier is typically a two- or three-letter string in Morse code...
/ILS
Instrument Landing System
An instrument landing system is a ground-based instrument approach system that provides precision guidance to an aircraft approaching and landing on a runway, using a combination of radio signals and, in many cases, high-intensity lighting arrays to enable a safe landing during instrument...
display is shown in relation to this figure. The heading indicator is slaved to a remote compass, and the HSI is frequently interconnected with an autopilot
Autopilot
An autopilot is a mechanical, electrical, or hydraulic system used to guide a vehicle without assistance from a human being. An autopilot can refer specifically to aircraft, self-steering gear for boats, or auto guidance of space craft and missiles...
capable of executing an approach by following the localizer and glide slope.
On a conventional VOR
VHF omnidirectional range
VOR, short for VHF omnidirectional radio range, is a type of radio navigation system for aircraft. A VOR ground station broadcasts a VHF radio composite signal including the station's identifier, voice , and navigation signal. The identifier is typically a two- or three-letter string in Morse code...
indicator, left/right and to/from must be interpreted in the context of the selected course. When an HSI is tuned to a VOR
VHF omnidirectional range
VOR, short for VHF omnidirectional radio range, is a type of radio navigation system for aircraft. A VOR ground station broadcasts a VHF radio composite signal including the station's identifier, voice , and navigation signal. The identifier is typically a two- or three-letter string in Morse code...
station, left and right always mean left and right and TO/FROM is indicated by a simple triangular arrowhead pointing to the VOR
VHF omnidirectional range
VOR, short for VHF omnidirectional radio range, is a type of radio navigation system for aircraft. A VOR ground station broadcasts a VHF radio composite signal including the station's identifier, voice , and navigation signal. The identifier is typically a two- or three-letter string in Morse code...
. 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.