Electronic flight instrument systems (EFIS) Basics Explained

airbus a320 PFD & ND image download
Airbus A320 PFD & ND

Electronic flight instrument systems (EFIS)

An Electronic flight instrument systems (EFIS) used in modern aircraft is a instruments data display system of underlying sensors, electronic circuitry, and software that effectively replaces all mechanical flight instruments and gauges with a single unit.. A primary flight display (PFD) or electronic attitude and direction indicator (EADI) and a navigation display (ND) or electronic horizontal situation indicator (EHSI) are part of the EFIS on larger aircraft (EHSI). For the captain and first officer, these instruments are duplicated.

EFIS Sensors Inputs

The EFIS (Electronic Flight Display System) uses important  input data from several sources including:


• Pitch, Roll, Heading rate and acceleration data from an Attitude Heading System Reference (AHRS) or Vertical Gyro (in conventional Aircrafts).

• Compass System (Magnetic compass System, IRS, GPS)

• Radar altimeter

• Air data system

• Distance Measuring Equipment (DME)

• Area Navigation System (RNAV)

• Vertical Navigation System (VNAV)

• Weather Radar System (WXR)

• Automatic Direction Finder (ADF).

A typical EFIS system comprises:

• Primary Flight Display (PFD)

• Navigation Display (ND)

• Display Select Panel

• Display Processor Unit

• Weather Radar Panel

• Multifunction Display

• Multifunction Processor Unit.

The Basic functions of Each EFIS Components

Here are the brief descriptions of each components.

EFIS primary flight display (PFD)

Airbus a320 PFD image download
Airbus a320 PFD

The basic EFIS PFD is a multicolor cathode ray tube (CRT) or liquid crystal display (LCD) display unit that shows VOR, localizer, TACAN (Tactical Air Navigation), or RNAV (Area Navigation) deviation, as well as glide slope or pre-selected altitude deviation. Other information like as mode annunciation, radar altitude, decision height, and excessive ILS deviation can be presented.

EFIS navigation display (ND)

Airbus a320 nd image download
Airbus A320 ND

A common EFIS ND is a multicolor CRT or LCD display unit, similar to the EFIS PFD. In this case, however, the display gives horizontal status information for the aircraft, which may include the following depending on the display mode selected: navigation source annunciation, digital selected course/desired track readout, excessive ILS deviation, to/from information, compass heading, selected heading, selected VOR, Localizer, or RNAV course and deviation (including annunciation or deviation type), navigation source annunciation, digital selected course/desired track readout, distance to station/waypoint, glide slope, or VNAV deviation, ground speed, time-to-go, elapsed time, or wind, course information, and compass heading/bearing pointer that can be driven by VOR, RNAV or ADF sources as selected on the display select panel of aircraft.

Display select panel (DSP)

The navigation sensor, bearing pointer, format, navigation data (ground speed, time-to-go, time, and wind direction/speed) are all selected on the display select panel, as well as VNAV (if the aircraft has this system), weather, and a second navigation source on the ND. There's also a DH SET control on the PFD that lets you set the decision height. The DSP also allows you to choose a course, a course direct to, and a heading.

Display processor unit (DPU)

The display processor unit processes and switches sensor input, generates the required deflection and video signals, and supplies power to the electronic flight displays. Two electronic flight displays with distinct deflection and visual signals can be driven by the DPU. A PFD on one display and an ND on the other is the for example.

Weather radar panel (WXP)

When Weather Radar is chosen on the MFD and/or the DSP, the weather radar panel includes MODE control (OFF, STBY, TEST, NORM, WX, and MAP), RANGE selection (10, 25, 50, 100, 200, and 300 nm), and system operating controls for the display of weather radar information on the MFD and ND. Display with Multiple Functions (MFD) another multicolour CRT or active-matrix LCD display device serves as the multifunction display. The weather radar (WXR) indicator is generally positioned on the instrument panel, and the display is normally mounted there as well. Weather radar, a pictorial navigation map, and, in some systems, a check list and other operational data are among the standard features presented by the device. In the event of a PFD or ND failure, the MFD can also show flight or navigation data.

Multifunction processor unit (MPU)

The sensor input processing and switching, as well as the necessary deflection and video signals for the multifunction display, are all handled by the multifunction processor unit. In the event that either or both display processing units fail, the MPU can send deflection and video signals to the PFD and ND displays.

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