22
INSTRUMENTATION — CHAPTER 22 · NOTES
Electronic Flight Information Systems
by Ghost Aviator
LECTURE PARTS
Table of Contents
- System Overview and Components
- Symbol Generators and Display Units
- Colour Display System
- EADI — Control Panel and Display
- Decision Height on EFIS
- EHSI — Control Panel and Display Modes
- EHSI Display Modes — VOR, ILS, MAP, PLAN
- Navigation Display Symbols
- Failure Annunciation
- Data Source Selection
- Practice Questions & Detailed Answers
1. System Overview and Components
EFIS presents attitude and navigation information on two electronic display units in a format easier to read and less likely to be misinterpreted than older mechanical instruments. It uses colour CRT or LCD displays.
A complete EFIS installation (left or right system):
- EADI — Electronic Attitude Director Indicator (or PFD — Primary Flight Display)
- EHSI — Electronic Horizontal Situation Indicator (or ND — Navigation Display)
- Control Panel
- Symbol Generator (SG)
- Remote Light Sensor Unit
2. Symbol Generators and Display Units
Symbol Generators (SGs) provide the analogue, discrete, and digital signal interfaces between aircraft systems, display units and control panel. They perform symbol generation, monitoring, power control, and main EFIS control functions.
Display units may be CRTs or LCDs. LCDs are smaller and generate less heat (less cooling needed). The PFD and ND are usually identical units for spares commonality — often interchangeable with systems display units (EICAS or ECAM).
3. Colour Display System
There is no set colour standard — colours may vary slightly between aircraft types. Typical colour assignments:
| Colour | Use |
|---|---|
| WHITE | Present situation information |
| GREEN | Present situation (where contrast with white needed); lower priority than white; engaged autoflight modes |
| MAGENTA (pink) | All "fly-to" information: flight director commands, deviation pointers, active flight path lines |
| CYAN (blue) | Sky shading on EADI; low-priority info such as non-active flight plan map data |
| YELLOW | Ground shading on EADI; caution information — failure warning flags, limit and alert annunciators, fault messages |
| RED | Heaviest precipitation levels on weather radar (WXR) |
Summary colour code for Navigation Displays:
- GREEN = engaged flight mode, dynamic conditions
- WHITE = present status, scales, armed flight mode displays
- MAGENTA = command information, pointers, fly-to condition
- CYAN = non-active and background information
- RED = warning
- AMBER = cautionary information, faults, flags
- BLACK = blank areas, display "off"
Remote Light Sensor
A photodiode that responds to ambient light on the flight deck and automatically adjusts CRT display brightness to an acceptable level.
4. EADI — Control Panel and Display
EADI Section of Control Panel
| Control | Function |
|---|---|
| BRT (Brightness) | Adjusts brightness of the ADI display |
| DH SEL (Decision Height Selector) | Selects desired decision height for DH alerting |
| DH RST (DH Reset) | Resets a DH alert on the associated ADI; changes RA display from yellow back to white |
| DH REF | Displays the selected decision height on both the controller and the EADI |
EADI Display Presentations
The EADI displays:
- Normal pitch and roll attitude from IRS
- Flight director commands
- Localizer and glide slope deviation
- Ground speed
- Radio altitude
- Decision height
- AFCS and Autothrottle modes
- Speed error scale (commanded vs. actual speed)
5. Decision Height on EFIS
DH and Radio Altitude presentation (Boeing-style):
- 2500–1000 ft AGL: RA shown as a digital read-out only
- Below 1000 ft: Display changes to a circular scale (calibrated in 100 ft increments); selected DH shown as a magenta marker on the outer scale; RA digital read-out inside the scale; scale segments are erased anticlockwise as aircraft descends
- At DH + ~50 ft: Aural alert chime sounds at increasing rate until DH is reached
- At DH: Marker and scale flash and change from magenta to amber/yellow
- DH RST pressed: Cancels alert chime, stops flashing, changes DH display back to normal colour (magenta)
Localizer / Glide slope exceedance: Deviation beyond normal ILS limits causes the scales to change colour to amber and the pointer to flash. Flashing ceases when the aircraft returns within limits.
Airbus/A300 style:
- RA shown at the base of the PFD centre display as digital numbers
- Above DH: green numbers
- Below DH: amber, slightly bigger numbers
- Enhanced by a voice warning system with manufacturer/airline-agreed height callouts
6. EHSI — Control Panel
| Control | Function |
|---|---|
| RANGE | Selects range for displayed navigation data and WXR |
| MODE SELECTOR | Selects display mode: VOR, ILS, MAP, PLAN |
| BRT (outer knob) | Main display brightness |
| BRT (inner knob) | WXR display brightness |
| MAP switches | In MAP mode: NAV AID, ARPT, RTE DATA, WPT overlays |
| EXP ARC | Selects VOR or ILS mode to show an expanded arc display |
| WXR | Enables weather radar data display in all modes except PLAN or full compass VOR/ILS |
7. EHSI Display Modes
Four principal display modes: VOR, ILS, MAP, PLAN. VOR and ILS can be either Full (full compass rose) or Expanded (arc — ~90° of compass rose).
Full VOR Mode
- Full compass rose; VOR source lower left, frequency lower right
- Magenta course needle pointing to selected course (150°)
- Deviation bar on ±2-dot scale
- TO/FROM pointer and annunciation
- DME distance top left; current heading in window; current track as white triangle on inside compass rose edge; selected heading as magenta "bug"
- Weather radar NOT available in full VOR mode
Expanded VOR Mode
- ~90° compass arc; white triangle at bottom = aircraft symbol
- Current track = white line from aircraft symbol tip to compass arc
- Weather radar AVAILABLE; when on, range arcs visible
- WXR shows: green (least turbulence), yellow, red (worst); magenta = turbulence mode if available
- Half-scale range displayed (e.g., selected 20 NM → displays 10 NM)
Full ILS Mode
- Full compass rose; ILS source lower left, frequency lower right
- Magenta course needle = localizer course; localizer deviation bar on exponential ±2-dot scale
- Glide slope deviation = magenta triangle moving on right-side scale
- Weather radar NOT available in full ILS mode
Expanded ILS Mode
- ~90° compass arc; localizer and glide slope deviations shown
- Weather radar AVAILABLE
Map Mode
MAP mode — the normal operating mode:
- Moving map background with all elements to a common scale
- Aircraft symbol at lower part of display; compass arc ±45° of instantaneous track at top
- Compass rose referenced to magnetic north between 73°N and 65°S; true north above these latitudes (or when TRUE selector used)
- Active route = magenta continuous line joining waypoints
- Active waypoint = magenta star; inactive waypoints = white star
- Distance and time to next waypoint shown at top
- WXR available; range arcs visible
- Curved trend vector (white, during turns) or altitude range arc (green, climb/descent)
- Off-route waypoints, airports, navaids shown in relative position
Plan Mode
PLAN mode:
- Static map background oriented to True North
- Used to review/check planned route changes before entering into FMC
- Arc at top = real-time (heading-up); planning section below = north-oriented
- Weather radar INHIBITED
- No wind speed/direction shown
WXR Summary — Mode Availability
| Mode | WXR Available? |
|---|---|
| MAP | ✅ Yes |
| Expanded VOR | ✅ Yes |
| Expanded ILS | ✅ Yes |
| Full VOR | ❌ No |
| Full ILS | ❌ No |
| PLAN | ❌ Inhibited |
8. Navigation Display Symbols
| Symbol | Colour | Meaning |
|---|---|---|
| Active Waypoint (star/name) | Magenta | Waypoint aircraft is currently navigating to |
| Inactive Waypoint (star/name) | White | Navigation point in active route (not current) |
| Off-Route Waypoint | Cyan | Waypoint not in active route |
| Airport | Cyan | Airport symbol |
| Tuned Navaid | Green | Currently tuned navigation aid |
| Unused Navaid | Cyan | Navigation aid not currently tuned |
| Wind direction/speed | White | Wind with respect to map orientation |
| Selected heading marker | Magenta | Heading set in MCP |
| Active route line | Magenta (solid) | Active route between waypoints |
| Active route modifications | White (dashed short) | Modified route pending activation |
| Inactive route | Cyan (dashed long) | Non-active stored route |
| T/C, T/D, S/C markers | Green | FMC-calculated Top of Climb, Top of Descent, Step Climb |
| North Pointer | Green | PLAN mode — confirms true north orientation |
| Altitude Range Arc | Green | MAP mode — predicts where reference altitude will be reached |
| WXR heavy precip | Red | Most intense radar returns |
| WXR medium precip | Amber/Yellow | Medium intensity returns |
| WXR light precip | Green | Lowest intensity radar returns |
| Turbulence mode | Magenta | Area of greatest activity in cloud (if turbulence mode available) |
9. Failure Annunciation
Failure of data signals (ILS, radio altimeter, etc.) is displayed on each EADI and EHSI as yellow flags "painted" at specific matrix locations on the CRT screens.
Fault messages may also appear: e.g., "WXR/MAP RANGE DISAGREE" if the flight management computer and weather radar range disagree with the control panel range data.
10. Data Source Selection
Pilots can independently connect their display units to alternate input data sources via a data source switch panel:
- Left or right Air Data Computer (ADC)
- Flight Management Computers (FMC)
- Flight Control Computers (FCC)
- Standby Inertial Reference Systems (IRS)
Practice Questions & Detailed Answers
Ghost Aviator Instrumentation — Chapter 22. DGCA CPL/ATPL.
Q1. The displays marked A, B, C, and D (refer to Annex A) are respectively:
✅ Correct Answer: D
Map mode has a moving map with aircraft at the bottom and compass arc at top. ILS full mode has a full compass rose with glide slope scale. Expanded VOR shows ~90° arc. Plan mode is static true-north orientated.
Q2. Refer to display E (expanded ILS). The correct statement is:
✅ Correct Answer: A
In expanded ILS mode, the heading shown in the window is 130°M. The localizer deviation bar being displaced indicates the aircraft is closing the localizer from the right. Glide slope triangle position above centre indicates the aircraft is above the glidepath.
Q3. On display D (Plan mode) the track from ZAPPO to BANTU is:
✅ Correct Answer: D
PLAN mode is always referenced to True North (not magnetic). The track from ZAPPO southward to BANTU in the plan view oriented to true north is 180°T (due south). The question of magnetic vs. true is resolved by the fact that PLAN mode is always True North oriented — heading references become tracks in °T.
Q4. On display C (expanded VOR/ILS) the centre of the weather returns is:
✅ Correct Answer: B
In expanded mode, weather returns position is read relative to the aircraft symbol at the bottom centre of the display. The centre of the WXR returns is positioned at approximately 332° relative (slightly to the left of the heading reference line) at approximately 13 NM range (based on the selected range scale).
Q5. The drawing shows the (i)... displaying (ii)... and (iii)...
(i) EADI / PFD / ND / EHSI (ii) 600 ft RA / 600 kt / 600 ft (iii) 200 ft DH / 200 ft AGL
(i) EADI / PFD / ND / EHSI (ii) 600 ft RA / 600 kt / 600 ft (iii) 200 ft DH / 200 ft AGL
✅ Correct Answer: C
The drawing shows an EADI (PFD/attitude indicator). At 600 ft the circular RA scale with digital read-out is displayed (below 1000 ft). 200 ft is the DH marker (magenta) on the RA scale. EADI = same as PFD in modern terminology.
Q6. The yellow "RA" symbol appears in place of the normal radio altitude display when:
✅ Correct Answer: C
Yellow flags/text on EFIS indicate faults or failure. A yellow "RA" flag means the radio altimeter data signal has failed — the RA display has been replaced by a yellow failure flag annunciation.
Q7. Symbols A, C, and E (in the symbol diagram) are best described respectively as:
✅ Correct Answer: D
Symbol A = magenta starred symbol = active waypoint (aircraft currently navigating to). Symbol C = navaid symbol (tuned navaid in green, unused navaid in cyan). Symbol E = cyan symbol not on active route = off-route waypoint.
Q8. When using EHSI, weather radar may be displayed on the following settings:
✅ Correct Answer: D
WXR is available on: MAP mode and EXPANDED VOR/ILS modes. WXR is NOT available on: Full VOR, Full ILS (full compass rose), or PLAN mode (inhibited). The key rule: WXR requires the expanded arc presentation or map mode — not the full compass rose or plan.
Memory tip: "Full compass = no weather." In full VOR/ILS mode the full compass rose takes up all the space. WXR data only overlays on the expanded arc or map background.
Q9. WXR display is controlled from:
✅ Correct Answer: D
EFIS is a two-sided system — Captain and First Officer each have their own EHSI control panel. WXR can be selected on/off from either pilot's EHSI control panel independently. Both CRTs can display weather radar simultaneously.
Q10. Decision height is adjusted and set on the:
✅ Correct Answer: C
Decision Height is displayed on the EADI (ADI) — the attitude indicator — not the HSI/EHSI (navigation display). Therefore the DH SEL (Decision Height Selector) is on the ADI/EADI section of the EFIS control panel.
Q11. Weather may be displayed, with modern EFIS, on:
✅ Correct Answer: D
Both the captain's and co-pilot's EHSI control panels have a WXR switch. Weather radar data can be displayed on both EHSI (ND) displays simultaneously. No special dedicated WXR screen is needed.
Q12. Airspeed is shown:
✅ Correct Answer: B
Airspeed (as part of speed error scale and ground speed) is displayed on the EADI (attitude indicator / PFD) — not on the EHSI (navigation display). Both captain's and first officer's EADIs display airspeed-related information.
Q13. With EFIS using IRS guidance, reference north can be:
✅ Correct Answer: B
The compass rose automatically references to magnetic north when between latitudes 73°N and 65°S, and switches to true north above these latitudes (where magnetic variation becomes extreme and unreliable). The crew may also manually select TRUE at any latitude.
Note the asymmetry: 73°N but only 65°S. This reflects real magnetic variation geography — the magnetic anomaly is more severe in the northern polar regions.
Q14. Modes available for EFIS HSI on some units are:
✅ Correct Answer: B
The four modes of the EHSI are VOR, ILS, MAP and PLAN. The question asks specifically about "some units" — MAP and PLAN are the two modes that require FMS data and are available only on equipped systems. VOR, ILS, MAP, and PLAN are the four standard modes. Answer B (MAP and PLAN) is what distinguishes this EHSI from a basic HSI.
Q15. The EFIS symbols for a navaid and en route waypoint are: (choose C)
✅ Correct Answer: C
Navaids use a circle or diamond symbol (green when tuned, cyan when unused). Waypoints use a star/asterisk symbol (magenta = active/current waypoint the aircraft is navigating to; white = inactive waypoint on active route; cyan = off-route waypoint).
Q16. An EFIS installation as well as having a control panel, symbol generators and a remote light sensor also has:
✅ Correct Answer: A
The five components of each EFIS system are: EADI (or PFD), EHSI (or ND), control panel, symbol generator, and remote light sensor. Therefore if you're given control panel + SG + remote light sensor, the missing components are EADI and EHSI.
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