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Electronic Flight Instrument System
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Electronic Flight Instrument System (EFIS)
An Electronic Flight Instrument System (EFIS) is a flight deck instrument display system in which the display technology used is electronic rather than electromechanical.
Early EFIS systems portray information using cathode ray tube (CRT) technology. Later instrument displays are presented on multi-colour liquid-crystal display (LCD) screens, which replace some or all of the conventional flight instruments for both pilots.
A typical EFIS system comprises an Electronic Attitude Direction Indicator (EADI) and an Electronic Horizontal Situation Indicator (EHSI). In some designs the two displays are integrated into one.
Electronic Attitude Direction Indicator (EADI)
This instrument depicts the information formerly displayed on an electromechanical Flight Director, together with vertical speed and, usually, altitude. Other information may also displayed according to the manufacturer's design.
In normal use, the EADI is coupled directly to the autopilot and the display is used by the pilot to monitor flight progress.
Alternatively, steering and attitude (pitch and roll) demand bars help the pilot to fly manually.
The EADI provide steering information to follow, for example:
- a manually input heading;
- a route input on the Flight Management System (FMS);
- a navigation beacon (VOR, ADF, etc.);
- an IRS (Inertial Reference System) track; or,
- an ILS localiser.
- climb or descend to a level and maintain that level on reaching;
- follow an ILS glidepath; or,
- follow a Go-around procedure;
In some cases, guidance is provided to assist the pilot to folow an ACAS RA.
Electronic Horizontal Situation Indicator (EHSI)
The Electronic Horizontal Situation Indicator (EHSI) replaces a number of different instruments found on a conventional aircraft, and may be used to depict some or all of the following information:
- heading flown;
- heading or track selected;
- bearing to or from a navigation beacon (VOR, DME);
- lateral deviation from a selected track;
- ground speed, distance and time to go;
- aeronautical map;
- weather information;
plus much more information according to design.