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Boeing 737 Electronic Flight Instrument System (EFIS) Chapter 23

EHSI CONTROLS

As shown in Diagram 2, the EHSI controls are to the right of the EFIS control panel.

RANGE — This selects the range for the navigation (MAP, CTR MAP, and PLAN) and
weather data display on the EHSI, the Flight Management Computer and Weather Radar.

Mode Select Switch — This selects the mode of data to be displayed on the EHSI.

BRT — Two concentric knobs consisting of the outer and inner controls:

The Outer Control adjusts the brightness of the HSI display.

The Inner Control adjusts the brightness of the weather radar display.

WXR — This is the weather radar ON/OFF switch. When the switch is in the on position,
weather radar information displays on the associated EHSI in the MAP, CTR MAP, and
EXP VOR/ILS, but not in FULL NAV, FULL VOR/ILS, or PLAN modes.

Map Mode Display Selector Switches — In the MAP, CTR MAP, or PLAN modes these
switches activate the display of the symbols listed below. Any or all of the switches can
be activated at the same time. When switched on, the switch illuminates (white).

VOR/ADF — This displays VOR/ADF bearing data in the MAP and CTR MAP modes.
When activated, this switch suppresses the MAP mode displayed ADF Bearing Pointer.

NAV AID — Navigation Aid data is displayed for VOR, VORTAC, etc. The FMC database
provides only the high altitude navigation aids when the 80 nm, 160 nm, or 320 nm range
scales are selected. All navigation aids display when using any of the other range scales.

ARPT — This displays all airports stored in the FMC database that are within the
viewable map area of the EHSI.

RTE DATA — This displays altitude constraints and the ETA for each active route
waypoint.

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Chapter 23 Boeing 737 Electronic Flight Instrument System (EFIS)

ELECTRONIC ATTITUDE DIRECTION INDICATOR

The EADI has one basic display mode, which shows:

¾ Aeroplane attitude
¾ Flight Director commands
¾ Various types of airspeed
¾ ILS
¾ Radio Altimeter

Across the top of the EADI, autothrottle and autopilot annunciations are provided when the
autopilot is either armed or engaged. An inclinometer (slip indicator) at the bottom of the EADI
provides turn and bank information.

Roll Indication

Autothrottle Pitch Pitch Roll Autopilot
Modes Indication Modes Modes Modes

THR HLD VNAV PTH HDG SEL FD Filled
Flight
Speed Tape 160 V1 20 20 Director
128 10 10 Command

140 Aeroplane
Symbol
1234 Glideslope
Deviation
10 10 Scale and
Pointer
PITCH ALT
H-Alert
GS 250 ROLL DH200
.765 1750 Decision
Height

Attitude Localizer Deviation Radio
Comparison Altitude

Alert

Scale Inclinometer

Diagram 3 – Typical EADI

EADI GENERAL

The EADI presents conventional EADI displays for:

¾ Attitude
• Pitch
• Roll

¾ Flight Director Commands
¾ Localiser and Glideslope deviation

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In addition, the EADI displays information relating to:

¾ Autoflight systems mode annunciations
¾ Aeroplane speed (VMO/MMO)
¾ Minimum speeds
¾ CAS
¾ Pitch Limit
¾ Mach Number
¾ Groundspeed
¾ Decision Height
¾ Radio Altitude

ATTITUDE DISPLAY

Attitude data is provided by the IRSs. The captain’s EADI uses the left IRS and the first officer’s
EADI uses the right IRS. The IRSs pitch and roll attitude information is valid through 360° of
rotation in each axis.

MODE ANNUNCIATIONS

Mode annunciations for the A/T and the AFDS appear at the top of the EADI displays.

FLIGHT DIRECTOR (F/D) COMMANDS

FD guidance commands from the selected FCC are displayed via split-axis flight director
command bars. The pitch and roll commands appear independently.

GLIDESLOPE (G/S) AND LOCALISER

(LOC) DEVIATION DISPLAYS

Glideslope and localiser deviation scales appear when a localiser frequency is tuned on the
associated VHF NAV receiver. A valid signal is required before the deviation pointer is displayed.

The normal localiser deviation scale is 1° per dot. When the course deviation is approximately 5/8
degree deviation (5/8 dot), and VOR/LOC is engaged, the scale automatically expands to indicate

½ degree deviation per dot. The scale remains expanded until:

¾ After landing rollout
¾ Go-around with a radio altitude greater than 200 ft

On a backcourse approach, the symbol generator reverses the polarity of the localiser deviation
pointer on the EADI. The reversal occurs when the aeroplane track differs from the selected MCP
course by more than 90°. When the frontcourse is set in the MCP display, the EADI and EHSI
course deviation display will agree on both a frontcourse and a backcourse approach.
Additionally, the glideslope scale does not display for a backcourse approach.

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Chapter 23 Boeing 737 Electronic Flight Instrument System (EFIS)

ILS DEVIATION WARNING
ILS deviation monitoring alerts the flight crew of excessive LOC or G/S deviations. This alerting
function is operative during single or dual A/P channel ILS approach. The alerting system is
armed when the aeroplane descends below 1500 ft radio altitude (RA) with the LOC or G/S
captured. If the captain’s or first officer’s LOC deviation exceeds ½ dot expanded scale or ¼ dot
standard scale the respective LOC scale changes colour from white to yellow and the miniature
runway stem flashes.
If the captain’s or first officer’s G/S deviation exceeds 1 dot deviation, the respective G/S scale
changes colour from white to yellow and the G/S pointer flashes. G/S deviation alerting does not
initiate below 100 ft RA, but continues below this altitude if the alert was triggered prior to descent
below 100 ft RA.

Each pilot’s alerting system self-tests upon becoming armed at 1500 ft RA. This self-test
generates a 2 second LOC and G/S deviation alerting display on each EADI.

RISING RUNWAY SYMBOL
The Rising Runway Symbol is an integral part of the LOC deviation display, and is positioned at
the top of the LOC Deviation Pointer. The Rising Runway Symbol displays in addition to the RA
display, giving an additional cue to the flight crew of the aircraft’s close proximity to the ground as
the aeroplane descends below 200 ft RA. Full scale, vertical movement of the Rising Runway
represents the last 200 ft of the radio altitude. Zero feet RA is indicated as the top of the Runway
Symbol rises to the base of the aeroplane symbol.

The requirements for display of the Rising Runway Symbol are as follows:

¾ Valid ILS/LOC frequency selected
¾ Valid RA data
¾ RA less than 2500 ft

If any of the above conditions are not met, the Runway Symbol does not display.

ATTITUDE COMPARATOR

A yellow PITCH or ROLL alerting annunciation is displayed on both EADIs if either symbol
generator detects a difference of more than 3° between the captain’s or first officer’s attitude
displays. A short time delay is incorporated to minimise nuisance annunciations.

DIGITAL RADIO ALTITUDE AND DECISION HEIGHT

When RA is less than 2500 ft, a digital display of radio altitude shows in the lower right hand
corner of the EADI. At all other times the digital RA display is blank.

When a positive decision height has been selected on the respective EFIS Control Panel, the
letters DH and the decision height are displayed just above the digital RA display of the
associated EADI.

When the aeroplane is below 1000 ft agl, an RA Dial is added to the radio altitude display and a
magenta pointer located on the radio altitude dial replaces the digital DH display.

When descending through the selected DH, a DH alert occurs. The RA dial, digital display, and
the DH pointer change colour to yellow, flash momentarily, then remain steady yellow as the
aeroplane continues to descend.

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Boeing 737 Electronic Flight Instrument System (EFIS) Chapter 23

The DH alert resets if any one of the following occurs:

¾ The DH reset switch on the EFIS control panel is pressed
¾ The RA increases to DH + 75 ft
¾ The radio altitude is equal to zero feet (touchdown)

Following an electrical power interruption, the DH value defaults to 200 ft.

MACH DISPLAY

The current Mach number from the respective Air Data Computer (ADC) displays if the following
are satisfied:

Accelerating Mach number is ƒ 0.40M
Decelerating Mach number previously above 0.4M and is still > 0.38M

GROUNDSPEED DISPLAY

There is a digital presentation of the current groundspeed. The groundspeed data comes from the
FMC or IRS with the FMC being the primary source. The numeric range is from 0 to 999 kt.

PITCH LIMIT SYMBOL

The position of the Pitch Limit Symbol is a function of the stall warning computer. The Pitch Limit
Symbol appears when the flaps are extended in any position.

During take-off, the Pitch Limit Symbol is fixed at 15° pitch attitude until the stall warning
computer commands a value greater than 15° (at approximately 100 kt). Above this speed, the
position of the Pitch Limit Symbol is a function of the various inputs to the stall warning computer
and is limited to a maximum of 30° of pitch.

In general, the Pitch Limit Symbol is programmed so that stick shaker activation coincides with a
pitch attitude equal to the Pitch Limit Symbol indication.

In a rapid pull up, the pitch attitude may exceed the Pitch Limit Symbol indication for a brief period
without initiating the stick shaker warning.

With a lightweight aeroplane, the low speed limit logic of the stall warning computer may activate
the stick shaker even with the Pitch Limit Symbol positioned slightly above the aeroplane symbol.

SPEED TAPE SCALE

The speed tape scale displays a range of approximately 84 kt. Numbers are placed on the tape at
20 kt intervals from 40 kt to 420 kt. The speed tape scrolls up and down and the digital readout
indicates current airspeed.

DIGITAL AIRSPEED READOUT

A digital readout of the current calibrated airspeed appears within the fixed airspeed reference
pointer. The units digit rolls continuously based on the current fractional unit value of the
calibrated airspeed to emulate the rolling digit readout of a conventional electrical/mechanical
airspeed indicator.

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Chapter 23 Boeing 737 Electronic Flight Instrument System (EFIS)

AIRSPEED TREND ARROW

The Airspeed Trend Arrow is a green arrow of variable length that points to the predicted
airspeed the aeroplane will achieve within the next 10 seconds, based on the present airspeed
and rate of acceleration. The Airspeed Trend Arrow does not display until its magnitude is greater
than 4 kt, and it disappears when its magnitude drops below 3 kt.

COMMAND SPEED

Command speed displays as a magenta, double-line cursor located on the speed tape scale if the
command speed is within the currently displayed speed tape range. The display shows the
numerical equivalent, above or below the speed tape scale, if the command speed is equivalent
to the selected speed on the MCP or the FMC command speed, whichever is applicable.

MAX OPERATING SPEED (VMO/MMO OR GEAR/FLAP PLACARDS)

A red and black barber pole represents the max operating speed. The position of the maximum
operating speed symbol is a function of data supplied to the SG from the stall warning computer.
The maximum operating speed is the lower of the:

¾ Gear extended placard speed
¾ Flaps extended placard speed
¾ VMO/MMO

HIGH-SPEED BUFFET MARGIN

The bottom of a hollow yellow bar that extends from the bottom of the VMO/MMO symbol at high
altitude represents the high-speed buffet margin. As the aeroplane climbs to altitudes above
25 000 ft, the yellow bar begins to extend to give an indication of the speed that would provide a
0.3G to high-speed buffet margin. At lower altitudes, the VMO/MMO speed is more limiting and the
high-speed buffet limit symbol is no longer visible. Since the stall warning computer uses FMC
gross weight to calculate the high-speed buffet margin speed, this display is not available if the
FMC is unable to compute gross weight.

NEXT FLAP PLACARD SPEED

The same symbol is used to represent this speed as is used to represent the high-speed buffet
margin. If the aeroplane is in the air and flaps are lowered, the hollow yellow bar extends from the
high-speed end of the speed tape. The end of the hollow yellow bar represents the placard speed
for the next normal flap position. Next flap placard speeds appear only for those flap positions
normally used during an approach and landing. The next flap placard symbol appears blank when
current flap position equals the selected landing flap configuration on the FMC/CDU APPROACH
REF page or when the flaps are in the process of retracting.

FLAPS UP MANOEUVRING SPEED

A small, green circle on the speed tape indicates the flaps up manoeuvring speed. This speed is
an output of the stall warning computer and is based on the actual gross weight as computed by
the FMC. It represents the best airspeed (climb or driftdown) for an aeroplane in the clean
configuration. This function is not enabled until the flaps are up.

V1 (DECISION SPEED)

Decision speed is depicted by a green -1 located opposite the V1 speed on the speed tape if the
V1 speed is within the displayed range. If the selected V1 speed is not within the displayed range,
a green V1 with the numeric value of the V1 speed appears at the high-speed end of the speed
tape.

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Boeing 737 Electronic Flight Instrument System (EFIS) Chapter 23

Before the V1 speed displays on the speed tape, the pilot must first enter the correct speed in the
scratch pad on the FMC/CDU TAKE-OFF page, and then line-select this speed to the V1 prompt
line.

VR (ROTATION SPEED)

VR speed is depicted by a green -R located opposite the rotation speed if the rotation speed is
within the displayed range. The symbol is blanked if the rotation speed is not within the displayed
range.

For VR to display on the speed tape, the pilot must first enter the correct speed in the scratch pad
on the FMC/CDU TAKE-OFF page and then line-select this speed to the VR prompt line.

VREF (REFERENCE SPEED)

The -R symbol represents the VREF speed. The FMC/CDU APPROACH REF page displays VREF
speed based on the current gross weight for three landing flap settings. The flight crew may
select the FMC computed speed or manually enter another value into the field corresponding to
the desired landing flap configuration. This speed then transmits via the FMC, causing the SG to
display the -R symbol opposite that speed on the speed tape.

The FMC updates the computed VREF speeds as fuel burns based on fuel totaliser inputs. A VREF
value does not update once it has been selected for transmission to the speed tape.

If the flight crew manually inserts a gross weight on the APPROACH REF page, the FMC
computed VREF speeds will be based solely on the manually entered gross weight as long as the
APPROACH REF page remains in view. A manually entered gross weight is not updated as fuel
burns off.

MINIMUM FLAP RETRACTION SPEED

A green -F on the right side of the speed tape indicates minimum flap retraction speed. The stall
warning computer computes this speed. It represents the speed that will provide the minimum
manoeuvre speed (depicted by the end of the low speed yellow bar) for the next normal flap
position (flap positions 5, 1, or UP only). The display will respond to the effects of extending the
flight spoilers.

MINIMUM MANOEUVRING SPEED

The end of the low-speed hollow yellow bar represents the minimum manoeuvring speed. If the
aeroplane is at low altitude and flies at this speed, it provides a 0.3G manoeuvre margin to stick
shaker. This allows for a 40° bank turn while manoeuvring in level flight.

If the aeroplane is at high altitude and flies at the minimum manoeuvring speed, it provides a
0.3G manoeuvre margin to low-speed buffet as opposed to a 0.3G manoeuvre margin to stick
shaker margin. Since the stall warning computer uses the FMC gross weight to calculate the
minimum manoeuvre speed at high altitudes, this symbol does not display at high altitude if the
FMC gross weight is not available. The display reflects the effect of extending the flight spoilers.

The hollow yellow bar is inhibited from take-off roll through the first flap retraction. Once the flaps
are up, the display shows for the remainder of the flight, including subsequent flap extensions.

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Chapter 23 Boeing 737 Electronic Flight Instrument System (EFIS)

STICK SHAKER SPEED

The end of the low-speed, red and black striped barber pole represents the stick shaker speed.
This speed represents the airspeed at which the angle of airflow vanes activates the stick shaker
warning. The source of the stick shaker airspeed is the stall warning computer. The display
reflects the effect of extending the flight spoilers.

EADI SYMBOLS Name Description
Aeroplane
Symbol Bank Indicator and Scale The EFIS SG provides a white
Sky/Ground/Horizon Line aeroplane attitude symbol
<
Pitch Scale White

The sky is cyan (light blue) and
the ground is yellow. The IRS
data control the sky/ground
movement and horizon line
(white).

A white scale (±90°) controlled
by IRS data. 0° indicates the
horizon line.

Flight Director Command A magenta symbol produced
by FCC data. Displays when
the respective Flight Director
(FD) switch is on and valid
command steering is available,
or during automatic operation
of the FD.

Localiser Pointer and Scale Blanks off when the FD switch
is off or when command
steering becomes invalid.

A magenta pointer with a white
scale and index that indicates
the localiser position.

The scale indicates the
deviation.

Expanded Localiser Scale When LOC is engaged and the
and Pointer deviation is slightly more than
½ dot the scale expands.

The pointer blanks when the
ILS localiser signal is too weak
to be usable.

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Boeing 737 Electronic Flight Instrument System (EFIS) Chapter 23

Symbol Name and Description
ALT
Glideslope Scale A magenta pointer with a white
DH 200 Pointer scale and index that indicates
1750 the glideslope position and the
Height Alert scale deviation.
GS 250
Decision Height and Radio The pointer does not display
Altitude when the glideslope signal is
unusable or when the track
and the front course on the
Main Control Panel (MCP)
differ by more than 90° (Back
Course).

A white display when Radio
Altitude (RA) is between 500
and 1000 ft. Reset by the DH
RST on the EFIS CP, or when
RA is greater than the height
alert value computed by the
EFIS SG

The decision height displays in
green. The DH is the one
selected on the EFIS CP when
the RA is above 1000 ft agl.

Appears blank when the DH is
negative

Radio Altitude displays in white
below 2500 ft agl.

The display is blank above
2500 ft agl.

The symbol colour changes to
yellow when below the
selected DH on descent.

Groundspeed The symbol colour changes to
white when passing DH +75 ft
during a go-around, after
touchdown, or after pressing
the RST switch on the EFIS
CP.

The FMC/IRS values are
displayed in knots and
coloured white

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Chapter 23 Boeing 737 Electronic Flight Instrument System (EFIS)

Symbol Name Description Mach
.765 Current Mach Number
Displays when the
increases above 0.4M.

Pitch Limit Symbol The Display is blank when the
Rising Runway Mach Number decreases
below 0.38M.

A yellow symbol that indicates
the pitch attitude that activates
the stick shaker.

A green symbol shaped like a
runway at the bottom of the
screen that displays when the
localiser pointer is in view and
the radio altitude is valid.

The symbol rises toward the
aeroplane symbol when radio
altitude is below 200 ft agl.

RADIO ALTITUDE DIAL

Diagram 4 – Radio Altitude

The digital display of Radio Altitude (white) is replaced with the dial when the aircraft is at or
below 1000 ft agl. A DH pointer (magenta) replaces the digital DH display.

¾ At or below 1000 ft agl the circumference of the dial increases or decreases
dependent on whether the aircraft is climbing or descending.

¾ The display changes colour to yellow and flashes momentarily when the aircraft
descends below DH.

¾ The DH Alert is reset automatically if the aircraft climbs 75 ft or more above the
selected DH or lands.

¾ Pressing the RST switch on the EFIS Control Panel manually resets the DH Alert.

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Boeing 737 Electronic Flight Instrument System (EFIS) Chapter 23

SPEED TAPES

V1 1 — V1 (decision speed) - Green
2 — FMC/MCP Command Speed - Magenta
160 128 3 — VR (rotation speed) - Green
4 — V1 (decision speed) - Green
140 5 — Speed Tape Scale - White

R

4

12

3

100

80

1. V1 Decision Speed

¾ Displayed in green
¾ Displayed after manual entry on the FMC/CDU TAKEOFF REF page
¾ V1 is only displayed in this location during the initial take-off roll when the

speed is beyond the displayed range

2. FMC/MCP Command Speed

¾ Displayed in magenta

3. VR Rotation Speed 5 – Speed Tape Scale - White

¾ Displayed in green
¾ Displayed after manual entry on the FMC/CDU TAKEOFF REF page

4. V1 Decision Speed

¾ Displayed in green
¾ Replaces the digital display in the top right corner of the speed tape when V1

is within the displayed range

5. Speed Tape Scale

¾ Displayed in white
¾ Scrolls up or down in response to the ADC calibrated airspeed
¾ Range 45 – 420 kt

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Chapter 23 Boeing 737 Electronic Flight Instrument System (EFIS)

250 6 — FMC/MCP Command Speed - Magenta
7 — Minimum Flap Retraction Speed - Green
180 8 — Minimum Manoeuvre Speed - Yellow
9 — Stick Shaker Speed - Red and Black
F

1630
15

2

140

120

6. FMC/MCP Command Speed

¾ Displays in magenta
¾ Displays in this position when the FMC/MCP Command Speed is above the

displayed range

7. Minimum Flap Retraction Speed

¾ Displays in green
¾ Displays on the speed tape during take-off or go-around

8. Minimum Manoeuvre Speed

¾ Displays in yellow
¾ The top of the yellow bar indicates the minimum manoeuvre speed
¾ The display is inhibited from the take-off roll until first flap retraction

9. Stick Shaker Speed

¾ Displays in red and black
¾ The top of the barber pole indicates the speed at which the stick shaker

activates

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Boeing 737 Electronic Flight Instrument System (EFIS) Chapter 23

220 10 — Flaps up Manoeuvering Speed - Green

200 11 — Rolling Digits Display - White
12 — Airspeed Trend Arrow - Green
3 13 — FMC/MCP Command Speed - Magenta

181820
160

140 134

10. Flaps up Manoeuvring Speed

¾ Displayed in green
¾ Shown when the flaps are up

11. Rolling Digits Display

¾ Displayed in white
¾ Indicates the current airspeed
¾ The position is fixed relative to the ADI position

12. Airspeed Trend Arrow

¾ The tip of the arrow depicts the predicted airspeed in the next 10 seconds
¾ The prediction is based upon present airspeed and acceleration

13. FMC/MCP Command Speed

¾ Displayed when the FMC/MCP Command speed is below the displayed
range

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Chapter 23 Boeing 737 Electronic Flight Instrument System (EFIS)

340 14 — Max Operating Speed - Red and Black
3230 15 — High Speed Buffet Limit - Yellow
31

2

300
280

14. Max Operating Speed

¾ Displayed in red and black
¾ Indicates VMO/MMO

15. High-Speed Buffet Limit

¾ Displayed in yellow
¾ The bottom of the yellow bar indicates the speed that provides a 0.3G

manoeuvre margin to high-speed buffet at high altitudes

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Boeing 737 Electronic Flight Instrument System (EFIS) Chapter 23

180 16 — Placard Speed - Red and Black
17 — Next Flap Position Placard Speed - Yellow
1630
15 18 — VREF Speed - Green

2 R

140

120

16. Placard Speed

¾ Displayed in red and black
¾ Indicates gear extended placard speed
¾ Flap extended placard speed for the selected flap position

17. Next Flap Position Placard Speed

¾ Displayed in yellow
¾ The bottom of the yellow bar indicates the flap extended placard speed for

the next normal flap position
¾ Displayed during flap extension

18. VREF Speed

¾ Displayed in green
¾ Indicates the VREF speed for the landing flap configuration as selected on the

FMC/CDU APPROACH REF page

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Chapter 23 Boeing 737 Electronic Flight Instrument System (EFIS)

EFIS – EADI FAULT DISPLAYS

OPERATION

If the specific input data to a symbol generator is identified as invalid data, the associated data or
parameter value blanks. In some cases yellow fault flags are displayed. The location, orientation,
and letter characters associated with each of these flags are shown below. The windshear
warning annunciation is displayed in red.

Diagram 5 – EADI Fault Displays

EADI FAILURE FLAGS AND ANNUNCIATIONS

1. Selected Speed Annunciation: The command speed and displays are inoperative

2. V1 Inoperative Annunciation: V1 display is inoperative
3. Speed Flag: The speed tape is inoperative

4. Speed Limit Annunciation: The displays associated with the stick shaker and
maximum operating speeds have failed

5. Mach Flag: The Mach number display has failed

6. Pitch Comparator Annunciation: The captain’s and first officer’s pitch angle displays
differ by more than 3°

7. Attitude Comparator Function Flag: The comparator function has failed

8. Localiser Flag: The localiser deviation display on the EADI has
failed

9. Windshear Warning Annunciation: The ground proximity computer has detected a
windshear condition

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Boeing 737 Electronic Flight Instrument System (EFIS) Chapter 23

10. Roll Comparator Annunciation: The captain’s and first officer’s bank angle displays

differ by more than 3°

11. Radio Altitude Flag: The radio altitude display has failed

12. Decision Height Flag: The selected decision height display has failed

13. Symbol Generator Fail Annunciation: The selected symbol generator has failed

14. Attitude Flag: The attitude display has failed

15. Flight Director Flag: The flight director has failed

EFIS TYPICAL EHSI CENTRE MAP, MAP, AND PLAN DISPLAYS

The EHSI can display selected FMC Data in three different selectable formats:

¾ CTR Map
¾ Map
¾ Plan

The format displayed depends upon the mode selected on the EFIS Control Panel (Diagram 6).

HSI

EXP
VOR /

NAV ILS

VOR/ MAP
ILS
FULL CTR
MAP
NAV

PLAN

BRT

Diagram 6 – EHSI Mode Selector

GENERAL
Each EHSI presents an electronically generated colour display of conventional HSI navigation
data:

¾ VOR/ILS Modes
¾ NAV Modes

Each EHSI is also capable of displaying the aeroplane’s flight progress on a plan view map:

¾ Map Mode
¾ CTR Map Mode

Or the aeroplane’s flight plan on a plan view map orientated to True North:

¾ Plan Mode

Excluding operation in the FULL NAV, FULL VOR/ILS and PLAN Modes, each EHSI also serves
as a weather radar display when the WXR Switch on the respective EFIS CP is on.

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Chapter 23 Boeing 737 Electronic Flight Instrument System (EFIS)

During normal operation, each EHSI receives information from its own symbol generator. Each
symbol generator receives data from a variety of aircraft systems to support the EHSI displays.

EHSI DISPLAY ORIENTATION
The various displays on the EHSI are orientated to aeroplane heading (heading up). With heading
up orientation, all displayed data references the aircraft heading as shown at the 12 o’clock
position on the compass rose.

During normal operation, heading reference data is supplied to each EHSI from the respective
IRS.

The FMC supplies aeroplane track data. If the FMC track data should become unreliable, the
respective IRS automatically supplies track data.

PLAN MODE
The PLAN mode is a map display which may be used to view an FMC flight plan route, either in
total for a short route, or waypoint by waypoint for a longer route. Its primary use is to set up the
flight plan conditions before flight. The upper part of the display describes the dynamic conditions
of the aeroplane:

¾ Track
¾ Selected and actual heading
¾ Distance
¾ ETA to the next waypoint

The lower part of the display is background data displaying the flight plan (Diagram 7).

23-22 Diagram 7 – PLAN Mode

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Boeing 737 Electronic Flight Instrument System (EFIS) Chapter 23

FEATURES OF PLAN MODE

¾ PLAN is selected on the EFIS Mode Selector Switch.
¾ A static map is displayed, oriented to true north with only 70° of the compass rose

showing.
¾ The top of the EHSI is the same in MAP Mode.
¾ The pilot can review the planned route by using the FMC/CDU LEGS page CENTER

STEP line select key.
¾ Weather radar data is inhibited.

MAP AND CTR MAP MODES
These modes display the aeroplane’s position with respect to the flight plan. The entire display is
dynamic, rotating as the aircraft moves. A triangle in the centre of the display represents the
aircraft. Waypoint and NAVAID symbols remain upright. Symbols which are rotated to maintain a
proper orientation are:

¾ ARPT (Airport)
¾ Holding pattern
¾ Procedural turn symbols

The displays are used to monitor the aeroplane’s position along the selected flight path.

Diagram 8 – Map Mode

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Chapter 23 Boeing 737 Electronic Flight Instrument System (EFIS)

FEATURES OF MAP MODE

¾ MAP is selected on the EFIS Mode Selector Switch
¾ The MAP mode display shows 70° of the compass rose

⊇¾ The aeroplane appears as a fixed symbol ( ) at the bottom of the display

superimposed on a moving map display
¾ The basic map background includes

• Origin/destination airports
• Flight plan route
• Display of navaids in use
¾ Optional background data is selected by using the Map Mode Display Selectors on
the EFIS Control Panel. This data includes:
• Off-route navigation aids
• Off-route airports
• Off-route named waypoints
• Tuned VOR/ADF radials
• Flight plan route waypoints
• ETAs
• Altitude constraints
¾ Weather radar returns are displayed when the WXR switch is ON

23-24 Diagram 9 – Centre Map Mode

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Boeing 737 Electronic Flight Instrument System (EFIS) Chapter 23

FEATURES OF CENTRE MAP MODE

¾ CTR MAP is selected on the EFIS Mode Selector Switch
¾ The CENTRE MAP Mode includes a 360° compass rose
¾ Displays the same data and symbols as the MAP mode
¾ The aeroplane symbol displays in the centre of the display so that MAP information

appears behind the aircraft

NAV MODE DISPLAYS

Selected FMC data can be shown by using the NAV Modes display. The display is referenced to
track and shows the aircraft position relative to:

¾ The next waypoint
¾ The vertical and horizontal flight path
¾ The NAV modes can have 70° or 360° compass displays

Diagram 10 - Expanded Navigation Mode

FEATURES OF EXPANDED NAVIGATION MODE

¾ EXP NAV is selected on the EFIS Control Panel Selector Switch
¾ The display shows lateral and vertical navigation guidance information similar to a

conventional HSI
¾ The FMC is the source of the navigation data
¾ Weather radar data is displayed when the WXR switch is on

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Chapter 23 Boeing 737 Electronic Flight Instrument System (EFIS)

Diagram 11 – Full Navigation Mode

FEATURES OF FULL NAVIGATION MODE

¾ FULL NAV is selected on the EFIS Control Panel Selector Switch
¾ Displays the same as EXP NAV except:

• Weather radar displays are not available
• The full compass rose is shown instead of the expanded compass rose
• Alternate symbols are used for the aeroplane symbol and course pointers

VOR AND ILS DISPLAYS
The VOR and ILS modes can be used with manually selected stations. The VOR mode is used
enroute with VOR and DME station inputs. ILS is the landing mode, and uses ILS and DME
station inputs. Appropriate deviations are displayed in both modes. The displayed heading is
magnetic below 73° north and 60° south latitude. At higher latitudes, the heading automatically
references to true north.

The difference between the heading and track line indicate drift angle.

For the VOR and ILS systems, the EHSI has two different types of displays which are selectable
on the EFIS Control Panel.

The FULL VOR/ILS displays include a 360° compass rose with the aeroplane symbol in the
center, and so are unable to display weather radar data.

The EXP VOR/ILS displays include only a 70° compass arc with the aeroplane symbol at the
bottom center. This display makes it easier to read the aeroplane’s heading and track values.
Additionally, these expanded displays can show the weather radar data.

Whether the display presents VOR or ILS data depends upon the VOR or ILS frequency selection
on the VHF NAV Control Panel.

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Boeing 737 Electronic Flight Instrument System (EFIS) Chapter 23

Except for the FULL and EXP display differences described above, the remainder of the
navigational data shown is the same on both types of displays. A detailed description of all
displayed symbols, parameters, and annunciations appears later in this chapter.

EXPANDED VOR MODE

D
D

Diagram 12 – Expanded VOR Mode

¾ VOR/ILS is selected on the EFIS Control Panel Selector Switch
¾ With a VOR frequency selected, VOR navigation data is displayed
¾ The navigation information is oriented to the aeroplane heading
¾ The source of the navigation data is displayed as VOR 1 or VOR 2 in the lower left

corner of the EHSI
¾ The TO/FROM annunciation and the navigation source frequency appear in the lower

right corner of the EHSI
¾ Weather radar return data and range arcs are displayed when the WXR switch is on

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Chapter 23 Boeing 737 Electronic Flight Instrument System (EFIS)
FULL ROSE VOR MODE

Diagram 13 – Full Rose VOR Mode

¾ FULL VOR/ILS is selected on the EFIS Control Panel Selector Switch
¾ The information displayed is the same as the expanded VOR mode with the following

exceptions
¾ Weather radar displays are not available
¾ A full compass rose shows instead of the expanded compass rose
¾ A drift angle pointer replaces the track line
¾ The TO/FROM pointer shows in addition to the TO/FROM annunciation
¾ Alternate symbols are used for aeroplane symbol and course pointer

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Boeing 737 Electronic Flight Instrument System (EFIS) Chapter 23
EXPANDED ILS MODE

Diagram 14 – Expanded ILS Mode

¾ VOR/ILS is selected on the EFIS Control Panel Selector Switch
¾ With an ILS LOC frequency selected, ILS navigation data is displayed with the

aircraft heading at the top.
¾ The source of navigation data (ILS 1/ILS 2) is shown in the lower left corner of the

EHSI
¾ The frequency of the navigation source is shown in the lower right of the screen
¾ Weather radar return data and range arcs are displayed when the WXR switch is on

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Chapter 23 Boeing 737 Electronic Flight Instrument System (EFIS)
FULL ROSE ILS MODE

Diagram 15 – Full Rose ILS Mode

¾ FULL VOR/ILS is selected on the EFIS Control Panel Selector Switch
¾ The information displayed is the same as the expanded mode with the following

exceptions

• Weather radar displays are not available

• A full compass rose is shown instead of the expanded compass rose

• A drift angle pointer replaces the track line

• Alternate symbols are used for aeroplane symbol and course pointer

EHSI SYMBOLOGY

Each EHSI may display the following symbols depending on the EFIS Control Panel selection.
The colours used are as follows:

Green: Active or selected mode and/or dynamic conditions
White: Present status situation and scales
Magenta: Command information, pointers, symbols, fly-to conditions, and weather
radar turbulence
Cyan: Non-active and background information
Red: Warning
Yellow: Cautionary information, faults, and flags
Black: Blank areas and off conditions

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Boeing 737 Electronic Flight Instrument System (EFIS) Chapter 23

Data Name Applicable Remarks
Colour Modes
Symbol Data Source
Aeroplane Symbol FULL VOR/ILS
White FULL NAV Aeroplane position is indicated
by the centre of the symbol
Full Compass Rose FULL VOR/ILS which is the centre of rotation
Display FULL NAV and translation for all the
Colour: White background and dynamic
(Low intensity display) symbols.

Source: EFIS SG

Displays 360° of IRS compass
data.

Source: IRS

Full Compass Rose CTR MAP Displays 360° of IRS compass
Display data.
Colour: White EXP VOR/ILS Source: IRS
(Low intensity display) MAP
EXP NAV Heading is from IRS
Expanded Compass EXP VOR/ILS 360° is available only 70° is
Rose MAP shown
Colour: White EXP NAV
CTR MAP The apex of the white triangle
Aeroplane Symbol indicates aeroplane position.
Colour: White The apex of the aeroplane is the
centre of rotation and translation
Heading Annunciator EXP VOR/ILS for all the background and
EXP NAV dynamic symbols.
Colour: Green MAP
CTR MAP The number under the low
Heading Readout and PLAN intensity index pointer is a
index heading.
Readout displays actual
Colour: White heading.
Compass is referenced to
(Heading index low magnetic north between 73°N
intensity) and 60°S.
Above these latitudes the
M/TRU Annunciator compass is referenced to true
north.
Colour: Green Source: IRS

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Chapter 23 Boeing 737 Electronic Flight Instrument System (EFIS)

Data Name Applicable Remarks
Colour Modes Symbol Data Source

Heading Annunciator FULL VOR/ILS Indicates number under pointer
Colour: Green FULL NAV is a heading.
Heading Readout and Box displays actual heading.
index All Modes Compass is referenced to
Colour: White magnetic north between 73°N
(Heading index low All Modes and 60°S.
intensity) Above these latitudes the
M/TRU Annunciator All Modes compass is referenced to true
Colour: Green north.
All Modes Source: IRS
Magnetic Status
Change All Modes Box appears for 10 seconds at
Colour: Green Box MAP transition to magnetic reference
around Green M NAV display.
annunciator VOR Source: SG
True Enhancement ILS
Annunciator Box surrounds TRU when
Colour: White box display is referenced to true
around Green TRU north unless yellow TRU
annunciator annunciator (below) is displayed
True Advisory Source: SG
Annunciator
Colour: Yellow box Yellow box surrounds TRU
around TRU (Initially flashes for 10 seconds)
annunciator when descent rate > 800 fpm for
2000 ft (landing phase)
Selected Heading The yellow box remains until
Marker and Line ascent rate > 500 fpm for 2000
Colour: Magenta ft (take-off phase)
Then changes to the white
Drift Angle Pointer enhancement annunciator
Colour: White above
Source: SG
Present Track
(Straight Trend Line) Manually positioned by heading
and Range Scale selector on the MCP.
Colour: White No dashed line on full displays
Source: FCC
Default: MCP

Indicates FMC/IRS computed
drift angle
Source: FMC
Default: IRS

Magnetic/true track which will
result with present heading and
winds.
Displayed range is ½ the actual
selected range.

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Boeing 737 Electronic Flight Instrument System (EFIS) Chapter 23

Data Name Applicable Remarks
Colour Modes Symbol Data Source
Range marks are used in CTR
CTR MAP MAP mode
Range arcs (not shown) are
Course Select Pointer VOR used in the MAP mode and in
and Vector the EXP VOR/ILS and EXP
NAV modes with WX selected
Colour: Magenta Track defaults to IRS for FMC
not valid
Runway Heading ILS
Pointer Indicates selected VOR course
when tuned to VOR source
Colour: Magenta Source: FCC
Default: MCP
White
Indicates selected runway
ALERT Desired Track Pointer NAV heading for front course when
and Vector NAV tuned to ILS source
Colour: Magenta Source: FCC
Default: MCP
Course Change
Annunciation Indicates desired track angle
Colour: Yellow from FMC or ANCDU

VOR Bearing Vectors MAP Displayed 10 seconds before
and Identifiers CTR MAP reaching waypoint.
Removed at reaching waypoint
Colour: Green Source: FMC or ANCDU

Course Deviation VOR Displayed when VOR/ADF
Scale selector on EFIS CP is pushed,
and associated DME not in
Colour: agility mode
Source: DAA
Scale – White
When VOR frequency tuned,
Bar - Magenta VOR course deviation is
displayed.
Localiser Deviation ILS One dot equals 5° deviation
Scale NAV Computed in the SG
Colour: Deviation = VOR Bearing minus
Scale – White selected course
Bar – Magenta
When ILS frequency tuned, ILS
Cross Track Deviation course deviation is displayed.
Colour: One dot is approximately 1°
Scale – White deviation
Bar - Magenta Source: DAA

Glideslope Deviation ILS When NAV mode is selected,
Radio Navigation indicates deviation from desired
track.
One dot is equal to 2 nm
Source: FMC

Displays glideslope deviation in

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Chapter 23 Boeing 737 Electronic Flight Instrument System (EFIS)

Data Name Applicable Remarks
Colour Modes Symbol Data Source
ILS mode.
Scale MAP One dot is approximately 0.35°.
Colour: CTR MAP NCD in backcourse
Scale – White Source: VHF NAV Unit
Bar - Magenta
Displayed when:
ADF Bearing Vectors VOR/ADF selector on EFIS CP
and Identifiers is pushed, or
Colour: Green In ADF mode
Source: ADF RCVR
DME 13.5 Left and Right ADF VOR
Pointers ILS Displayed in ADF mode and if
VOR 1 (2) Colour: Green NAV ON switch on ADF CP is on
ILS 1 (2) PLAN Source: ADF RCVR
Reciprocal Left and
NAV Right ADF Pointers VOR Displays distance to tuned DME
110.10 Colour: Green ILS station
116.80 Two resolutions:
or AUTO DME Distance Resolution 1: Whole nm if
Colour: White distance >100 nm
Resolution 2: tenths of a
Selected Radio Nav VOR nautical mile if distance < 100
Source ILS nm
Source: DAA
Colour: Green
Displays selected Radio Nav
FMC Selected NAV mode based on the EFIS CP
Colour: Green mode selection or frequency
from DAA
ILS Frequency Display ILS Radio Nav source is based on
Colour: Green source select programme pins
on EFIS SG
VOR Frequency VOR
Colour: Green Display indicated source of NAV
DATA.
Source: FMC

Displayed when a valid ILS
frequency is being received
Source: DAA

The VOR frequency is displayed
when a valid VOR frequency is
manually tuned
The word AUTO is displayed
when the VOR frequency is
automatically tuned by the FMC
Source: DAA

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Boeing 737 Electronic Flight Instrument System (EFIS) Chapter 23

TO (FROM) Data Name Applicable Remarks
Colour Modes Symbol Data Source

TO/FROM VOR Indicates whether the selected
Annunciator course will take the aeroplane
Colour: White MAP TO or FROM the selected VOR
CTR MAP station
Wind Direction and NAV Source: EFIS SG
Speed VOR
ILS Indicates wind speed in knots
Colour: White Wind direction is with respect to
MAP the display reference (magnetic
BUGLE Waypoint and ID CTR MAP or true north)
Colour: White PLAN Displayed when wind speed is
NAV
Active Waypoint ƒ 6 kt
Colour: Magenta MAP Source: FMC
Route CTR MAP Default: IRS
Colour: see right PLAN
Identifier listed below and right
27.5 NM Bearing to Waypoint NAV of the standard waypoint
and Vector Source: FMC
Colour: Magenta MAP
CTR MAP Name of active waypoint
Distance To Go PLAN Source: FMC
(DTOGO) NAV
Colour: White The active route is displayed
MAP with continuous MAGENTA
0834.4Z ETA Display CTR MAP lines between waypoints
Colour: White PLAN Inactive routes in CYAN with
NAV long dashes between waypoints
FMC/IRU Position MAP Changes to the active route are
Difference CTR MAP displayed in white dashes
Colour: White NAV between waypoints
When the route change is
Radio Navigation executed on the CDU, the short
dashes are replaced with a
continuous magenta line
Source: FMC

Indicates bearing to active
waypoint
Source: FMC

Distance to an active waypoint:
Resolution 1: Whole nm if
DTOGO >100 nm
Resolution 2: tenths of a nm if
DTOGO < 100 nm
Source: FMC

Indicates time of arrival at an
active waypoint
Source: FMC

The SG computes the position
difference between the FMC
and each IRU

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Chapter 23 Boeing 737 Electronic Flight Instrument System (EFIS)

; KTEB Data Name Applicable Remarks
Colour Modes Symbol Data Source
If either position difference
Airport and ID MAP > 12 nm, the SG displays the
Colour: Cyan CTR MAP magnitude and direction of both
PLAN position differences
Route Data MAP The position difference arrow
Colour: same as CTR MAP points to the IRU position
waypoint symbol PLAN L or R indicates which IRS
present position the displayed
Navaids and ID: MAP position difference corresponds
VOR CTR MAP to.
DME/TACAN PLAN
VORTAC Non-flight plan airports are
Colour: MAP displayed when ARPT switch
Untuned – Cyan CTR MAP selected
Tuned - Green PLAN Source: FMC
Tuned Navaid and MAP
Selected Course CTR MAP ALT and ETA for active
Colour: Green PLAN waypoints (with ID) displayed
MAP when route data switch on EFIS
Non-Flight Plan CTR MAP CP is on
Waypoint and ID PLAN Source: FMC
Colour: White MAP
Airport, Runway and CTR MAP Non-flight plan navaids
ID PLAN displayed when NAV AID switch
Colour: White on EFIS CP on.
Source: FMC
Runway and ID Select course source: FCC or
Colour: White MCP

When navaid is manually tuned
Selected course and its
reciprocal are displayed
Source: FMC

Non-flight plan waypoints
displayed when WPT switch on
Source: FMC

Selected on FMC CDU
Displayed when EHSI range is
80 nm, 160 nm or 320 nm
Source: FMC

Selected on FMC CDU
Displayed when EHSI range is
10 nm, 20 nm, or 40 nm
Source: FMC

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Boeing 737 Electronic Flight Instrument System (EFIS) Chapter 23

Data Name Applicable Remarks
Colour Modes Symbol Data Source

Holding Pattern MAP Displayed when a holding
Colour: CTR MAP pattern is selected as part of the
Inactive – Cyan PLAN route
Active – Magenta Source: FMC
Modified - White PLAN
Display below track tape is
North Up Pointer MAP referenced to True North
Colour: Green CTR MAP Source: FMC
NAV
Vertical Deviation Displays vertical deviation from
Scale and Pointer vertical profile during VNAV
Colour: descent mode
Scale – White One dot equals 400 ft deviation
Pointer - Magenta For deviation greater than 440 ft
pointer is at end of scale and, in
Selected Reference MAP addition, a digital readout
Point (SRP) With ID CTR MAP appears below the scale if
and Radials PLAN aeroplane is above flight path.
If aeroplane is below flight path
Colour: Green digital readout is above scale
Source: FMC or ANCDU
Selected Reference MAP
Point (SRP) With ID CTR MAP Displayed as a selected
and Distance Circle PLAN reference point (fix) via the FMC
CDU
Circle: Green Can be with any number of
special map symbols (e.g. VOR,
Range to Altitude Arc MAP VORTAC, Airport, etc.).
Source: FMC
Colour: Green CTR MAP
Circle representing selected
; T/D ; S/C Altitude Profile Points MAP distance displayed around SRP
; T/C ; E/D Colour: Green CTR MAP Selected distance indicated
PLAN below circle
Source: FMC
Curved Trend Vector MAP
Colour: White CTR MAP Curved arc represents the point
where MCP selected altitude will
Radio Navigation be reached if current vertical
and lateral flight path angles are
maintained
Source: FMC

Calculated by FMC
T/D – Top of Descent
S/C – Step Climb
T/C – Top of Climb
E/D – End of Descent
Source : FMC

Segmented curve predicts the
directional trend
It is calculated by the SG

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Chapter 23 Boeing 737 Electronic Flight Instrument System (EFIS)

Data Name Applicable Remarks
Colour Modes
Symbol Data Source
Weather Radar MAP
Returns CTR MAP Based on present position,
EXP NAV groundspeed and cross track
Colour: As for AWR EXP VOR acceleration
EXP ILS
It shows the predicted position
VAR/WX Weather Radar Mode MAP at the end of 30, 60, and 90
VAR/WX + t Colour: Green CTR MAP seconds
VAR/MAP EXP NAV
Weather Radar EXP VOR The number of segments
TEST Antenna Tilt EXP ILS represented:
Colour: Green
+ 12 MAP Range > 20 nm - 3 segments
CTR MAP
EXP NAV Range 20 nm – 2 segments
EXP VOR
EXP ILS Range 10 nm – 1 segment

Multi-coloured returns are
presented when EFIS CP WXR
ON switch is pushed

Most intense areas are
displayed in red, turbulence in
magenta

Source: WXR XCVR

Displayed when weather radar
is turned on

VAR/ is displayed when variable
gain is selected

Source: WXR XCVR

Displayed when weather radar
is turned on

Source: WXR XCVR

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Boeing 737 Electronic Flight Instrument System (EFIS) Chapter 23

EHSI SYSTEM FAILURE FLAGS AND ANNUNCIATION

Whenever specific input data to a symbol generator is identified as invalid data, the associated
symbol, or parameter value, goes blank. In all cases flags and annunciations are in yellow.

Diagram 16

HDG — This flag indicates that the heading data has failed

RANGE DISAGREEMENT ANNUNCIATIONS
Three sets of words can be used to show range disagreements:

¾ WXR RANGE DISAGREE indicates that the selected range on the EFIS Control
Panel is different from the WXR display (as above).

¾ MAP RANGE DISAGREE indicates that the selected range on the EFIS Control
Panel is different from the MAP display range (see later diagrams).

¾ WXR/MAP RANGE DISAGREE indicates that the selected range on the EFIS
Control Panel is different from the MAP and WXR display range (see later diagrams).

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Chapter 23 Boeing 737 Electronic Flight Instrument System (EFIS)

WEATHER ANNUNCIATIONS

¾ WXR FAIL indicates weather radar has failed (no weather data displayed).

¾ WXR WEAK indicates a weather radar calibration fault.

¾ WXR ATT indicates loss of attitude stabilisation for antenna.

¾ WXR STAB indicates weather radar stabilisation is off.

¾ WXR DSPY indicates loss of Display Unit cooling or an overheat condition of the HSI.
Weather Radar display is blanked

VTK (Vertical Track Flag) indicates a failure of the FMC vertical track data.

VOR or LOC displays if the EXP VOR/ILS mode is selected.

XTK (Cross track deviation flag) displays if the EXP NAV Mode is selected.

XXXXX Possible annunciations are:

¾ RT
¾ ANT
¾ CONT
¾ ATT
¾ WEAK
¾ STAB

Only when WXR TEST fails.

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Boeing 737 Electronic Flight Instrument System (EFIS) Chapter 23

Diagram 17

Diagram 18 23-41

MAP indicates selection of the MAP Mode.

Radio Navigation

Chapter 23 Boeing 737 Electronic Flight Instrument System (EFIS)

Diagram 19

VOR 1 (VOR Flag) indicates failure of a VOR Display on the EHSI. This function displays if the
MAP or CTR MAP Mode is selected and the VOR/ADF map switch is on.

Diagram 20

EXCESS DATA indicates the refresh rate of the MAP Display has dropped below limits. The
display may flicker at lower refresh rates.

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Boeing 737 Electronic Flight Instrument System (EFIS) Chapter 23

INSTRUMENT TRANSFER SWITCHING

During normal operation, each pilot’s EFIS display utilises independent IRS and SG inputs. The
EFI Transfer switch determines the SG source for both displays.

¾ With the EFI transfer switch in the normal position the Number 1 SG provides display
symbols for the captain’s EFIS displays, the Number 2 SG provides display symbols
for the first officer’s EFIS displays.

¾ If the EFI transfer switch is in the BOTH ON 1 position, both sets of displays utilise
the Number 1 SG.

¾ If the EFI transfer switch is in the BOTH ON 2 position, both sets of displays utilise
the Number 2 SG.

The IRS transfer switch selects the IRS that supplies inputs to the respective SG as well as other
aeroplane systems.

¾ With the IRS transfer switch in the normal position, the left IRS provides inputs to the
Number 1 SG and the right IRS provides inputs to the Number 2 SG

¾ If the IRS transfer switch is positioned to BOTH ON L, the left IRS provides data to
both SGs

¾ If the IRS transfer switch is positioned to BOTH ON R, the right IRS provides data to
both SGs

LIGHT SENSING AND BRIGHTNESS CONTROLS

There are two sets of ambient light sensors that automatically adjust the brightness of the EADI
and EHSI displays. The captain’s and first officer’s displays are adjusted independently. Two
remote light sensors, located on the instrument glare shield, adjust the brightness of the
associated EADI and EHSI as a function of the light coming through the forward windows. Two
integral light sensors, located in the EADI and EHSI instrument bezels, work in parallel to adjust
the brightness of the EADI and EHSI displays as a function of ambient light shining on the face of
either display.

Manual adjustment of the display brightness, above or below the brightness level set by the
automatic system, is accomplished by adjusting the brightness controls on the associated EFIS
Control Panel.

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Chapter 23 Boeing 737 Electronic Flight Instrument System (EFIS)

23-44 Radio Navigation

GENERAL

Four component systems comprise the Flight Management System (FMS):

¾ Flight Management Computer System (FMCS)
¾ Autopilot/Flight Director System (AFDS)
¾ Autothrottle (A/T)
¾ Inertial Reference Systems (IRSs)

PILOTS

AFDS IRSs

A/T

V NAV L NAV
ON ON

ACARS COMMANDS
FMC

COMPUTATIONS

CDUs

INTEGRATED FMS OPERATION CONDITION: L NAV AND
INDEPENDENT OPERATION V NAV ENGAGED
ACTIVE
INACTIVE

FMS SCHEMATIC

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Chapter 24 Boeing 737 Flight Management Computer (FMC)

Each of these components is an independent system, usable individually or in various
combinations. The term FMS refers to the concept of joining these independent components
together into one integrated system that provides continuous:

¾ Automatic navigation
¾ Guidance
¾ Performance management.

In essence, the FMS is capable of four-dimensional area navigation (Latitude, Longitude, Altitude,
Time) while optimising performance to achieve the most economical flight possible.

The integrated FMS provides centralised cockpit control of the aeroplane’s flight path and
performance parameters. The Flight Management Computer, or FMC, is the heart of the system,
performing navigational and performance computations and providing control and guidance
commands. The automatic management features of the FMC eliminate many routine tasks and
manual computations previously performed by the pilots. However, the pilots must still monitor
the FMC to ensure compliance with the planned route of flight.

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Boeing 737 Flight Management Computer (FMC) Chapter 24

OPERATION OVERVIEW

The two Multi-Function Control Display Units (MCDUs) allow the crew to enter the desired flight
plan routing and performance parameters into the FMC. FMC navigational and performance
computations then display on the MCDUs for reference or monitoring. Related FMC commands
for lateral and vertical navigation may be coupled to the AFDS and A/T through the Mode Control
Panel (L NAV and V NAV). The IRSs and other aeroplane sensors provide additional required
data. MCDUs also permit interface with the ACARS system.

When radio updating is not available, the FMC uses the IRS position as a reference. This mode
of navigation, referred to as IRS NAV ONLY, displays a message to warn the flight crew that
navigation accuracy may be less than required. During IRS NAV ONLY operation, the FMC
applies an automatic correction to the IRS position to determine the most probable FMC position.
The FMC develops this correction factor by monitoring IRS performance during periods of radio
updating to determine the IRS error. Flight crews should closely monitor FMC navigation during
periods of IRS NAV ONLY operation especially when approaching the destination. The accuracy
of the FMC navigation should be determined during the descent phase of flight by using radio nav
aids and radar information if available.

Inaccurate radio updating may cause the FMC to deviate from the desired track.

The crew may select any degree of automation desired. This can mean simply using the CDU
Data Displays for reference during manual flight, or using conventional autopilot functions, or
selecting full FMS operation with automatic flight path guidance and performance control.

Even with full FMS operation, management and operation of the aeroplane is always under the
total control of the flight crew. Certain functions can only be implemented by the pilots, such as:

¾ Thrust initiation
¾ Take-off
¾ Altitude selection
¾ ILS tuning
¾ Aeroplane configuration
¾ Landing rollout

The flight crew should monitor FMC navigation throughout the flight to ensure that the desired
route of flight is being accurately followed by the automatic systems.

The following schematic presents a simplified depiction of how the various FMS components
interrelate.

The Flight Management Computer System, with its Control Display Units (FMC/CDU), provides
the pilots with a flight management tool which performs navigational and performance
computations. Computations related to lateral navigation include items such as:

¾ Courses to be flown
¾ ETAs
¾ Distance to go

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Chapter 24 Boeing 737 Flight Management Computer (FMC)

For vertical navigation, computations include items such as:

¾ Fuel burn data
¾ Optimum speeds
¾ Recommended altitudes

When operating in the Required Time of Arrival (RTA) mode, the computations include:

¾ Required speeds
¾ Take-off times
¾ Route progress information

In addition, the FMC also provides control and guidance commands that can be coupled to the
AFDS and A/T. This allows integrated FMS operation with automatic lateral and vertical
navigation from initial climb to final approach.

CDU FUNCTION

CDU PAGE DISPLAY GENERAL

The page displays a single page of FMC data, as selected by a function and mode key or a line
select key.
The Ambient Light Sensor automatically adjusts the Display contrast for ambient light conditions.
The Brightness Control adjusts the brightness of the display by rotating the knob.

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Boeing 737 Flight Management Computer (FMC) Chapter 24

FUNCTION AND MODE KEYS

Pressing the Mode keys selects the appropriate page of FMC data for the
display.

The EXECute key executes the display data.

LINE SELECT KEYS
There are 6 keys on either side of the screen (Left 1L – 6L, Right 1R – 6R). Each key is
associated with its adjacent data line. (See diagram below).

Press — If the scratch pad is blank, pressing the line select key moves appropriate
moveable data on the line into the scratch pad.

If appropriate data already exists in the scratch pad, then that data transfers up the line (if
modifiable) and replaces any previous data.

If the line has the access prompt symbol < or > the display changes to the indicated new
page, or the indicated function is accomplished.

If the line is a procedure, the procedure is selected.

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Chapter 24 Boeing 737 Flight Management Computer (FMC)

KEYBOARD

SP key inserts a space into the scratch pad when pressed.
± key enters a minus sign(-) into the scratchpad that changes to a plus sign (+) with a second
press.
Delete Key causes the word DELETE to appear in the scratch pad (if previously blank).
Subsequent line selection to a deletable line deletes that line (in some cases, execution is also
required).
CLR Key clears scratch pad data from this CDU only, or clears CDU Messages.

Momentary Press clears the last character keyed-in, or clears a message.
Press and Hold clears all characters.
Slash (/) Key enters a / character in the scratch pad. This function serves to separate data
entries for speed/altitude, etc.
Main Keyboard enters the alpha-numeric characters into the scratch pad.

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Boeing 737 Flight Management Computer (FMC) Chapter 24

CDU PAGE DISPLAY

PERF INIT: Page title
1/2 Top Right of Screen:
The first digit identifies the page number (from
Box Prompts: within a group of related pages) presently being
Dash Prompts: displayed.
2LData Line Title/ Data Line (line):
_ _ _ _ _ _ _ _ _ _ _ Display Division: The second digit identifies the total number of
Scratch Pad: related pages (if any) which are available for
display using the PREV PAGE or NEXT PAGE
keys.

Identify a line requiring data entry for FMC
operation.

Identify a line where is data entry optional. Such
entries help to optimise FMC computations.

When displayed, the title identifies the type of
data displayed on the line below.

Page data displays above the dashed line.
Various prompts and the scratch pad appear
below the line.

The bottom line of the display. Displays CDU
messages, Keyboard entries, or data being
transferred between lines or pages within the
line select keys.

Selecting a new page does not affect scratch
pad entries.

Radio Navigation 24-7

Chapter 24 Boeing 737 Flight Management Computer (FMC)

PAGE STATUS

Page Status indicates the active or modified status of certain route or performance data (active
route shown above).

If the page data is inactive, Page status is blank.

FUNCTION AND MODE KEYS

CLB: The Climb Mode Key displays various climb pages that allow evaluation and/or change of
the climb mode.

CRZ: The Cruise Mode Key displays various cruise pages that allow evaluation and/or change
of the cruise mode.

DES: The Descent Mode Key displays various descent pages that allow evaluation and/or
change of the descent mode.

EXEC: The Execute Function Key is the FMC command key.

Illuminated (White) indicates that data entered on a page may now be activated. The
data can consist of required entries, or be a proposed modification to the active route or
performance data. If a modification, the original (unmodified) data is still active.

Pressing the EXEC key activates the data or modification and extinguishes the light bar.

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Boeing 737 Flight Management Computer (FMC) Chapter 24

PREV PAGE The previous page or next page function keys. When pressed, the display
or changes to the next lower or next higher page number within a multiple page
NEXT PAGE: group of related pages.

N1 Limit Displays a page with engine N1 limit values and allows the pilot to select thrust
Mode Key: limits if automatic selection is not desired. The active limit is always available for
display on the N1 indicators and for use by the autothrottle.

INIT REF: Initialisation/Reference Mode Key displays pages used for initialising the FMC
and IRSs, plus other pages containing various categories of reference data.

RTE: The route mode key displays pages used to enter or revise the origin,
destination, departure runway and each route segment of the flight plan route.
MENU: Also displays procedures selected on the Departures/Arrivals pages.
DEP/ARR:
HOLD: The route is entered manually or as a stored company route.
PROG:
The Menu Key provides access to sub-systems such as FMC, ACARS, etc.

The Departure/Arrival Mode Key displays the pages for listing terminal area
procedures for a selected airport and permits the selection of departure and
arrival/approach procedures for entry into the flight plan route.

The Hold Key displays the pages for any previously defined holding patterns, or
allows initial development of holding patterns for entry into the active route. It is
also used to exit a holding pattern.

The Progress Mode Key, when pressed, displays pages with current dynamic
data concerning progress along the active route, including ETAs and fuel
remaining estimates for the next two waypoints, destination, and the next altitude
change point.

This also provides information on wind, temperature, TAS, Route Tracking, and
the status of the IRSs and DME/VHF Nav Radios.

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Chapter 24 Boeing 737 Flight Management Computer (FMC)

It also allows access to the RTA PROGRESS page for the initialisation and
monitoring of the RTE Mode.

LEGS: The Legs Mode Key displays pages containing lateral and vertical details for
FIX: each leg of the flight plan route. It allows revision of individual waypoints and
certain speed/altitude crossing restrictions.

The Fix Mode Key displays pages used for determining ETA at, distance to, and
altitude at the intersection of the active route and a radial or distance from any
waypoint/fix. It also allows determination of present radial and distance from any
waypoint/fix.

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