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Electronic Flight Instrument System | Overview


An electronic flight instrument system (EFIS) is an electronic display technology on the flight deck display system. It usually consists of Engine Indicating and Crew Alerting System (EICAS), Primary Flight Display (PFD) and Multi-Function Display (MFD) display. They commonly use a liquid crystal display (LCD) even though they earlier used cathode ray tube (CRT) displays.

Installation of the EFIS varies greatly this is where a wide-body aircraft is equipped with six or more display units on which flight and navigation data are displayed while a light aircraft is likely to have one unit.

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The installation of EFIS follows the sequence:
• Displays
• Controls
• Data processors

Basic EFIS contains all the facilities in one unit.

Display Units

• Primary flight display (PFD)
• Navigation display (ND)/Multi-function display (MFD)
• Electronic centralized aircraft monitoring (ECAM)/Engine indications and crew alerting system (EICAS)

Control Panels

There is the provision of controls to the pilots where they select the display mode and range (for instance, compass rose or maps) and key in data (like a certain heading).

The pilots only need to enter the selection once, and the data busses broadcast the inputs for use by other equipment. For instance, the pilot makes a selection of the preferred level-off altitude on the control unit. The EFIS repeats the altitude selected on the Primary flight display (PFD), and it generates an altitude error display by comparing it with the actual altitude. The altitude selection is also used by altitude alerting system to deliver appropriate warnings, and by automatic flight control system for leveling off.

Data Processors

The symbol generator also known as display processing computer or display electronics unit, produces the visual display in the EFIS. It receives data inputs from the pilot and the EFIS format selections made, and signals from sensors. This generator does not only generate symbols but also has the monitoring facilities, a display driver (hardware not software) and a graphics generator. The input arrives through data buses, and are verified. The computations required are performed, and the display driver and graphics generator produce the entries to the display units.

Monitoring in EFIS Like ordinary the computers, the flight instrument systems require a continuous self-monitoring and power-on-self-test facilities. The systems, however, requires additional monitoring competencies like:
Input validation — validate each data from the sensor.
Data comparison — verify the inputs from the duplicated sensors
Display monitoring — identify instrument system failures

Former display Practice (electromechanical)

The electromechanical displays are fitted out with synchro mechanisms which transmitted, to the pitch, an instrument comparator, roll and heading which is shown on the First Officer’s and Captain’s instruments. The comparator notified the excessive differences between the two displays (Captain and First Officer). Even an error like far downstream (referring to the data flow direction; from the sensor to the processor, to display), the roll system triggers a warning in the comparator. The instrument comparator is, therefore, providing both display monitoring and comparator monitoring making a huge difference in the EFIS.


Comparator Monitoring

The comparator task in the electronic flight instrument system (EFIS) is to give warnings for airspeeds, roll, pitch, and altitude indications. It checks if the roll data from sensor 1 is the same as the roll data from sensor 2 where if not, it puts a warning caption on both PFDs. With advanced EFIS systems, more comparator monitors are enabled.

Display Monitoring

An EFIS display lets no easy re-transmission of what is shown. This requires a new approach to the display monitoring that gives safety equal to that of a traditional system. One solution is keeping the display system simple, such that the errors are minimal as possible where the unit will either works or not work. The errors should always be obvious and not insidious. Now monitoring function can be moved upstream to the symbol generator output.

In this system, each generated symbol has two display monitoring channels. The internal channel, from its symbol generator, samples the output to the computer and display unit, for instance, what roll attitude produces the indication. The computed roll attitude is at that point compared with the input of the roll attitude to the symbol generator from the AHRS (Attitude and Heading Reference System) or INS. Any difference is most likely led by error processing and initiates a warning on display.

The same check carried out by the deck external monitoring channel on the symbol generator on the flight’s other side: the symbol generator of the Captain checks the First Officer’s symbol generator, the First Officer’s inspects the Captain’s. If any symbol generator notices a fault, it puts up an alert on its display.
The external monitoring channel also checks the sensor inputs to the symbol generator for reasonableness. A false input, like a radio height more than the radio altimeter’s maximum, fallouts in a warning.

Route information

Route information is displayed in the bottom and right of the navigation screen. The following information is displayed in the bottom of the screen on three pages:

– destination waypoint information;

destination waypoint information

– The nearest airspace border;

nearest airspace border

– The next airspace border.

the next airspace border

Press the ENCODER to switch the pages.

Flight plan information is located in the right part of the screen.

In the top right of the screen, the next waypoint information is displayed in purple: its ICAO index, bearing, distance to it and ETA (or ETE depending on the device settings). Below the same information about the next four waypoints is displayed in grey.

OBS (Omni-bearing Selector) mode

OBS (Omni-bearing Selector) mode switches off consequent shifting of waypoints and always keeps the destination waypoint active.

When in OBS mode, the course to the destination waypoint of the flight plan is displayed on the navigation screen as a line going through this waypoint. The longer beam pointing the OBS course is displayed in light blue. The shorter beam of a back bearing is displayed in blue.

EFIS OBS mode screen

OBS course value is displayed in light blue on the course indicator on the flight information screen or in light blue on the OBS indicator navigation screen. For OBS course the device calculates cross track error which is displayed on the top of the navigation screen on the XTK indicator, and on the flight information screen, it is displayed as vertical yellow line and a digit value on the attitude indicator.

How to switch OBS mode:

  • 1) Press button [ III ] on the flight information screen or on the navigation screen to open menu;
  • 2) Select “OBS Approach” to set up OBS course;
  • 3) Select the required course in the course setting window by rotating the ENCODER
    (pressing the ENCODER [ I ] adds 45° to the course value and helps to select the required course quickly);
  • 4) Press button [ I ] once to set the course;
  • 5) Press [ II ] to switch off OBS mode;
  • 6) Press [ III ] to cancel selection and close OBS setting window.

how to set OBS approach

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