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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 a Primary Flight Display (PFD) (Electronic Attitude Direction Indicator (EADI)) and an Electronic Horizontal Situation Indicator (EHSI) (Navigation Display). In some designs the two displays are integrated into one.

EFIS Boeing 737
Example of a flight deck with electronic flight information displays

Primary Flight Display (PFD)

EADI
Primary Flight Display.

The Primary Flight Display (PFD) is an instrument which integrates and depicts, on a single display, all of the information that was historically presented on a number of individual electromechanical instruments. The PFD has evolved from a basic attitude indicator/flight director combination, presented electronically on a CRT, to an Electronic Attitude Direction Indicator (EADI) which, variable by manufacturer, added additional information such as heading, altitude and airspeed. The modern PFD displays virtually all of the information that the pilot requires to determine basic flight parameters (altitude, attitude, airspeed, rate of climb, heading, etc) plus autopilot and auto-throttle engagement status, flight director modes and approach status. Depending upon the phase of flight and pilot selections, the flight director will provide appropriate lateral guidance to maintain the selected track, heading or approach and missed approach track and vertical guidance for climb and descent, level off, approach and missed approach. This greatly reduces pilot workload while in manual flight and facilitates flight monitoring with the autopilot engaged as all required information is displayed on a single instrument.

Integrated PFD / EHSI, Source: Orbcore Media Intl., LLC

In most cases, guidance is provided on the PFD to assist the pilot in folowing an ACAS RA.

Electronic Horizontal Situation Indicator (EHSI)

The Electronic Horizontal Situation Indicator (EHSI), often referred to as the Navigation Display (ND), replaces a number of different instruments found on a conventional aircraft instrument panel, 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.

EHSI
Figure illustrating the use of a typical EHSI in navigation mode and in weather mode.

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