DGCA CPL / ATPL Study Notes • Radio Navigation • Ch 17

✈ Chapter 17: EFIS
Electronic Flight Information System

📋 Contents

1. Introduction 2. EFIS Components 3. EHSI Controller 4. Display Modes 5. EHSI Colour Coding 6. EHSI Symbology 7. Interpreting Displays 8. EFIS Summary 9. Practice Questions (9 Q)

1. Introduction

The Electronic Flight Information System (EFIS) replaces conventional electromechanical flight instruments with colour electronic displays. The EHSI (Electronic Horizontal Situation Indicator) displays navigation, radar and TCAS information in multiple selectable modes. EASA AMJ CS-25 governs colour coding and display requirements.

Fig 17.1: EFIS overview — EADI/PFD (left) and EHSI/ND (right) with symbol generator inputs

📡 EHSI Inputs

VOR (frequency, radial, deviation)
DME (distance, groundspeed)
ILS (localizer and glideslope deviation)
ADF (relative bearing)
FMS/FMC (waypoints, track, flight plan route)
AWR (weather radar overlay)
TCAS (traffic advisories)

All inputs are processed by Symbol Generators which output the display format.

2. EFIS Components

Fig: EFIS architecture — dual symbol generators feeding port and starboard EHSI and EADI displays

📡 EFIS System Architecture

Component	Function
EADI / PFD	Electronic Attitude Director Indicator / Primary Flight Display — attitude, airspeed, altitude, VSI, ILS deviations
EHSI / ND	Electronic HSI / Navigation Display — heading, track, bearing pointers, waypoints, weather
Symbol Generator	Processes all sensor inputs into display symbols for EHSI and EADI
EFIS Controller	Pilot interface — mode selection, range, data overlays (WXR, VOR, ARPT etc.)
EICAS/ECAM	Engine/systems monitoring display (Boeing/Airbus respectively)

3. EHSI Controller

Fig: EFIS controller panel — mode selector, range knob, overlay switches (WXR, VOR, ARPT, WPT, etc.)

📡 EHSI Controller Functions

Control	Options / Effect
Mode Selector	ILS, VOR, MAP, PLAN (selects display format)
Range Selector	Selects scale of display (10, 20, 40, 80, 160, 320 NM)
WXR switch	Enables weather radar overlay (Expanded VOR/ILS and MAP modes only)
STA/VOR	Display tuned VOR/ADF radials
NAV AID	Display navigation aids (VOR, NDB symbols) from database
ARPT	Display airports from database
WPT	Display waypoints on MAP mode
RTE DATA	Display route data (ETAs, fuel predictions) at waypoints
TCAS switch	Toggle TCAS traffic display on/off; press to clear TCAS FAIL message

4. Display Modes

EHSI mode options — Full Rose VOR, Expanded VOR, Full Rose ILS, Expanded ILS, MAP, PLAN

📡 EHSI Display Modes

Mode	Description	WXR/TCAS	Orientation
Full Rose VOR	360° compass rose; VOR course/deviation; two bearing pointers	✗	Heading-up
Expanded VOR	Arc display (~120° arc); VOR course, DME, deviation bar; range arcs shown	✓	Heading-up
Full Rose ILS	360° rose; ILS course/localizer deviation; glideslope on EADI	✗	Heading-up
Expanded ILS	Arc display; ILS/LOC course deviation; range arcs shown	✓	Heading-up
MAP	Moving map centered on aircraft; waypoints, airports, route, weather	✓	Heading-up
PLAN	Static map of flight plan; waypoints, airports, NAVAIDs; NOT heading-up	✗	True North-up

⚠ Key Points

WXR and TCAS: only displayable in Expanded VOR/ILS and MAP modes
PLAN mode is North-up; all others are Heading-up (magnetic or true)
Range arcs (white): displayed in expanded modes when WXR on, and MAP at all times
MAP mode selectable overlays: VOR/ADF, NAV AID, ARPT, RTE DATA, WPT, WXR, TCAS

Fig 17.2: Expanded VOR mode — aircraft position relative to VOR, DME distance, heading, track, wind

Fig 17.3: Full Rose VOR mode — bearing pointers, VOR1/VOR2 select, CDI deviation

Fig: Expanded ILS mode — LOC deviation bar, range arcs, weather overlay, heading bug

Fig: MAP mode — waypoints, airways, airports overlaid on moving map with range rings

Fig: PLAN mode — north-up static flight plan display; aircraft position shown as symbol

5. EHSI Colour Coding (EASA CS-25)

📡 Standard EHSI Colours

Colour	Used For
YELLOW/AMBER	Caution/advisory; items requiring attention but not immediate action
RED	Warnings; immediate action required; flight envelope exceedances
GREEN	Normal operation; active armed mode annunciation; on-course deviation
WHITE	Present values, scales, range arcs, heading information
CYAN/BLUE	Sky on EADI; engaged modes; selected altitude above present
MAGENTA	Active flight plan path; FMS/LNAV command bars; active waypoints

⚠ Colour Rules (CS-25)

RED used only for warnings — never for advisory or normal information
AMBER/YELLOW for cautions and non-normal conditions only
System must ensure no confusion between colours or symbols is possible
Critical information (attitude, altitude, heading) must not be lost or inaccurately displayed

6. EHSI Symbology

EHSI symbology guide — aircraft symbol, bearing pointers, range arcs, course bar, TCAS intruders

📡 Key EHSI Symbols

Symbol	Meaning
⇧ (aircraft symbol)	Own aircraft position; heading shown by nose direction
Course deviation bar	Lateral deviation from selected course (1 dot = typically 2° VOR or 0.5° LOC)
VOR1 bearing pointer (single)	Bearing to selected VOR1
VOR2/ADF pointer (double)	Bearing to VOR2 or ADF
Heading bug (cyan)	Selected heading (MCP/FCU heading select)
Wind arrow & velocity	Current wind direction and speed
Range arc (white)	Distance markers from aircraft; scale-dependent
TCAS traffic (cyan/amber/red)	Intruder aircraft; proximity advisory (cyan), traffic advisory (amber), resolution advisory (red)

7. Interpreting EHSI Displays

✓ Reading an Expanded VOR Display (Typical Exam Q)

Example: VOR2 selected, 116.80 MHz. Aircraft outbound from beacon, 13.3 NM (DME). 7.5° right of required track 165°(M). Heading 130°(M), track 133°(M). Heading bug 104°(M). WXR on WX+T mode, 12° uptilt, cloud 105°(M) at 8–17 NM. Scale 20 NM. Wind 126°(M)/20 kt.

Course deviation bar is 7.5° to the LEFT of aircraft symbol → aircraft is 7.5° RIGHT of track
Bearing pointer points behind aircraft (outbound from VOR)
Weather contour centred at 105°(M) — shown as coloured return from radar

8. EFIS Summary

Parameter	Detail
EHSI inputs	VOR, DME, ILS, ADF, FMS, AWR, TCAS
Processor	Symbol generators (port and starboard)
Display modes	Full Rose VOR/ILS, Expanded VOR/ILS, MAP, PLAN
WXR/TCAS display	Expanded VOR/ILS and MAP modes only
PLAN mode orientation	North-up (true); all others: heading-up
Active route	Magenta
Warnings	Red only
Cautions	Amber/yellow
Normal/scales	White
Active modes	Green
FMS commands	Magenta
Standard	EASA CS-25 AMJ 25-11

9. Practice Questions

Q1. The orientation of the PLAN mode of an EHSI display is:

(a) magnetic north-up

(b) track-up

(c) true north-up

(d) heading-up

Answer: (c)
PLAN mode is oriented to true north-up. All other EHSI modes (VOR, ILS, MAP) are heading-up.

Q2. Weather radar information can only be displayed in:

(a) MAP mode only

(b) expanded VOR/ILS and MAP modes

(c) all modes

(d) full rose and MAP modes

Answer: (b)
WXR (weather) and TCAS can only be displayed in Expanded VOR/ILS and MAP modes.

Q3. The colour used for the active FMS flight plan path on an EHSI is:

(a) green

(b) white

(c) magenta

(d) cyan

Answer: (c)
The active FMS flight plan path is shown in magenta. Green = normal/active modes. White = scales/present values. Cyan = sky/selected altitude/heading bug.

Q4. The EHSI symbol generator receives inputs from:

(a) VOR, ILS, DME only

(b) VOR, ILS, DME, ADF, FMS, AWR, TCAS

(c) FMS only

(d) ILS and VOR only

Answer: (b)
Symbol generators process inputs from: VOR, DME, ILS, ADF, FMS, AWR, and TCAS.

Q5. According to EASA CS-25, which colour is used exclusively for warnings:

(a) amber

(b) green

(c) white

(d) red

Answer: (d)
Red is used exclusively for warnings requiring immediate action. Amber/yellow for cautions. Green for normal operations. White for scales.

Q6. Range arcs on the EHSI are displayed in:

(a) MAP mode only

(b) all modes at all times

(c) expanded VOR/ILS when WXR selected, and MAP mode always

(d) full rose modes only

Answer: (c)
Range arcs (white) displayed in expanded VOR and ILS modes when WXR is ON, and in MAP mode at all times.

Q7. On the EHSI Expanded VOR display, the aircraft is shown 7.5° to the right of track 165°. The course deviation bar will appear:

(a) 7.5° to the left of the aircraft symbol

(b) 7.5° to the right

(c) directly ahead

(d) behind the aircraft

Answer: (a)
If the aircraft is to the RIGHT of track, the course bar (track) is displaced to the LEFT of the aircraft symbol — same as a CDI where the needle deflects toward the selected course.

Q8. The TCAS switch on the EHSI controller, when pressed with TCAS already displayed:

(a) increases TCAS range

(b) removes TCAS from display

(c) changes TCAS mode

(d) has no effect

Answer: (c)
Pressing TCAS when displayed removes TCAS information. When TCAS FAIL is displayed, pressing it removes the message.

Q9. Selectable overlays available in MAP mode include:

(a) VOR/ADF, airports, waypoints, weather

(b) ILS only

(c) weather only

(d) waypoints and ILS only

Answer: (c)
In MAP mode, the selectable overlays are: VOR/ADF radials, NAVAIDs, airports, waypoints, route data, weather (WXR), and TCAS.

DGCA CPL/ATPL Radio Navigation Study Notes
Chapter 17 — EFIS (Electronic Flight Information System)
Capt Pankaj Pahil | www.ghostaviator.com
For personal study use only.

✈ Chapter 17: EFISElectronic Flight Information System