Updated: Sep 18, 2020
Electronic Flight Instrument System
most modern passenger aircraft use Electronic Flight Instrument System (EFIS) displays in what has become known as the ‘glass cockpit’. EFIS provides large, clear, high-resolution displays which are easy to view under wide variations of ambient light intensity. Displays can be independently selected and configured as required by the captain and first officer and the ability to display information from various data sources in a single display makes it possible for the crew to rapidly assimilate the information that they need. A notable disadvantage of EFIS is a significant increase in EMI . The two most commonly featured EFIS instruments are the Electronic Horizontal Situation Indicator (EHSI) and the Electronic Attitude Direction Indicator (EADI) .
The EFIS uses input data from several sources including:
• TACAN (see later)
• pitch, roll, heading rate and acceleration data from an Attitude Heading System Reference (AHRS) or conventional vertical gyro
• compass system
• 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.
A320 PFD and ND brightnessand transfer controls
The Primary Flight Display (PFD) is a multicolour CRT or AMLCD displaying aircraft attitude and flight control system steering commands including VOR, localizer, TACAN, or RNAV deviation; and glide slope or pre-selected altitude deviation. The PFD provides flight control system mode annunciation, auto-pilot engage annunciation, attitude source annunciation, marker beacon annunciation, radar altitude, decision height set and annunciation, fast-slow deviation or angle-altitude alert, and excessive ILS deviation.
The Navigation Display (ND) provides a plan view of the aircraft’s horizontal navigation situation. Data includes heading and track, VOR, ILS, or RNAV course and deviation (including annunciation or deviation type), navigation source annunciation, to/from, distance/direction, time-togo, elapsed time, course information and source annunciation from a second navigation source, and weather radar data. The ND can also be operated in an approach format or an en-route
format with or without weather radar information included in the display.
Operational display parameters (such as ground speed, time-to-go, time, and wind direction/speed) can be selected by means of the Display Select Panel (DSP).
The Multifunction Display (MFD) is a colour CRT or AMLCD . Standard functions displayed by the unit include weather radar (in which the colours green, yellow and red are used to indicate increasing levels of storm activity), pictorial navigation map, check lists and other operating data. In the event of a failure of any of these displays, the required information can be shown on the displays that remain functional.
The Display Processor (DPU)/Multifunction Processor Unit (MPU) provides sensor input processing and switching for the necessary deflection and video signals, and power for the electronic flight displays. The DPU can drive up to two electronic flight displays with different deflection and video, signals
Multifunction Display (MFD)
Electronic Flight Instrument System (EFIS)
The flight instruments were the first to adopt computer technology and utilize flat screen, multifunctional displays (MFD). EFIS uses dedicated signal generators to drive two independent displays in the center of the basic T. The attitude indicator and directional gyro are replaced by cathode ray tubes (CRT) used to display EADI and EHSI presentations. These enhanced instruments operate alongside ordinary mechanic and electric instruments with limited integration. Still, EADI and EHSI technology is very desirable, reducing workload and panel scan with the added safety provided by integration of navigation information as described.
Early EFIS systems have analog technology, while newer models may be digital systems. The signal generators receive information from attitude and navigation equipment. Through a display controller, the pilot can select the various mode or screen features wishing to be displayed. Independent dedicated pilot and copilot systems are normal. A third, backup symbol generator is available to assume operation should one of the two primary units fail.
Figure . A simplified diagram of an EFIS system. The EADI and EHSI displays are CRT units in earlier systems. Modern systems use digital displays, sometimes with only one multifunctional display unit replacing the two shown. Independent digital processors can also be located in a single unit to replace the three separate symbol generators.
Electronic depiction of ADI and HSI information is the core purpose of an EFIS system. Its expanded size and capabilities over traditional gauges allow for integration of even more flight instrument data. A vertical airspeed scale is typically displayed just left of the attitude field. This is in the same relative position as the airspeed indicator in an analog basic T instrument panel. To the right of the attitude field, many EFIS systems display an altitude and vertical speed scale. Since most EFIS EADI depictions include the inclinometer, normally part of the turn coordinator, all of the basic flight instruments are depicted by the EFIS display
Figure An EFIS EADI displays an airspeed scale to the left of the horizon sphere and an altimeter and vertical speed scale to the right. The slip indicator is the small rectangle under the direction triangles at the top. This EFIS display presents all of the flight information in the conventional cockpit basic T.