B737 Flight Instruments & Displays

Overview

The CDS supply information to the six display units.

They include:

• 2 Primary Flight Displays
• 2 Navigation displays
• Upper Display Unit
• Lower Display Unit

In addition to the displays, following are included as a backup:

• Standby compass
• Integrated Standby Flight Display

Common Display System

The DUs provide flight and engine information to the pilots from the CDS.

The Upper Display Unit displays engine and fuel indications, as well as crew alert messages. The Lower Display Unit operates with the ability to switch between secondary engine parameters and hydraulic system information.

ADIRU

Air Data Inertial Reference Units.

Provides the following information to the instruments, engines, B737 Flight Controls, FMC, and all other systems requiring inertial and air data.:

• Position
• Speed
• Altitude
• Attitude

The system includes two IRUs (Left and Right) which contain internal gyros and accelerometers for position information.

Other components of the ADIRS include:

• 4 Air Data Modules
• 1 Inertial System Display Unit
• 1 Mode Select Unit

Two main pitot tubes and four static ports provide pressure information for for speed and altitude. Two Alpha Vanes provide AoA information, and a Total Air Temperature probe provides air temperature to the ADIRS system.

This information is sent to the flight displays by two DEUs.

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DEU

Display Electronic Unit

The DEUs are computers and distribute information from various aircraft sensors and systems. The data is converted to digital signals and sent to the displays.

During normal operation DEU 1 supplies information to:

• CA’s DUs
• upper DU

While DEU 2 provides information to:

• FO’s DUs
• lower DU

Should either DEU fail, the other DEU will automatically control the other side. It allows all displays to use a single DEU source. *Note that while operating on a single DEU, each pilot still receives information from independent sources and both ADIRUs..

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EFIS

Electronic Flight Instrument System

With the DISPLAYS CONTROL PANEL switch in the NORMAL position, the left EFIS Control panel operates the captain’s flight instruments, while the right EFIS Control Panel operates the FO’s instruments. Should a panel fail, all displays are controlled by the remaining EFIS Control Panel.

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CDS Faults

There are three messages that display when there is a fault in the CDS or DEU system:

Fault message	Interpretation	Conditions	Color
CDS FAULT	Non-dispatchable fault in the CDS system	Ground only prior to second engine start	AMBER
CDS MAINT	Dispatchable fault in CDS system	Ground only prior to second engine start	WHITE
DSPLY SOURCE	A DEU has failed after both engines started or airborne	After both engine starts	AMBER

Primary Flight Display

Each pilot’s PFD is normally located on the outboard DU.

Each PFD contains:

• Flight Mode Annunciator
• Autopilot, Flight Director System Status indicator
• ADI
• RADALT
• ILS
• Heading/Track
• ASI/MACH
• Altitude
• VSI

Each PFD displays attitude information from the aircraft’s ADIRU system.

In addition to standard data, the ADIs also provide Pitch Limit Indications that indicate the maximum pitch limit for the current configuration. Going beyond the PLI results in stick shaker activation, and is displayed when the flaps are not up or at slow speeds with the flaps up.

On the speed tape, the maximum speed bar is displayed in red and is adjusted to meet the lowest of:

• Vmo/Mmo with gear and flaps up
• 320 kts when gear down (max gear extended speed)
• Flap limit during each flap extension

The minimum speed bar shows the speed at which the stick shaker will activate, based on gross weight, flap setting, and bank angle.

Additionally, the tape includes a green Speed Trent Vector that computes expected speed within 10 seconds. There are also amber max/min manoeuvring speed indications.

With flaps up, the Maximum Maneuvering Speed indication gives the pilots an additional 0.3g maneuver margin protection to high speed buffet. This may be displayed at high altitude with flaps up and relatively high gross weights.

The minimum speed amber tape displays the flap limit placard speed for the next normal setting, assuming a sequence of 1, 5, 15, and 30.

Control Display Unit

The CDUs are the primary means for interaction between the flight crew and the FMC.

Each CDU page displays up to 6 data lines, along with respective line titles. Line select keys are used to modify the data on any given line; selecting it copies the data into the scratchpad so that they can be modified.

It is also possible to enter data into the scratchpad first and then press a line key to copy the data into that line.

Note that thrust reductions for climb are capped at 25% N1. CLB-1 indicates a 3% thrust reduction (or 10% N1), CLB-2 indicates a 6% reduction (or 20% N2).

Active CDU data being used by the autoflight system is displayed in magenta.

CDU Conventions

Data entry is accomplished using different methods:

• Via scratchpad with alphanumeric keys
• Transferred to scratchpad from a data line

Data from the scratchpad is transferred to a data line by selecting the adjacent LSK.

Note that the scratchpad must be empty in order to use the LSKs to copy data into it. Additionally, typing characters will overwrite FMC-generated messages on the scratchpad.

Pages containing boxes indicates that data entry into that field is mandatory, such as the PERF INIT page during preflight since performance calculations are not possible until entries are made into these fields.

Dash prompts indicate data that is either:

• Optional
• Used for additional calculation or information

Large fonts displayed on the CDU indicate manually entered information or mandatory altitude restrictions. Small fonts indicate predicted altitude values. Note that only large font altitude data values can be deleted.

When large font values are deleted, they are replaced by a predicted value based on constant angle descents.

Entering altitudes can be done in the FL200 or simply 200 format. For altitudes below 1,000 ft a leading zero is required.

An A suffix indicates altitudes to be flow at-or-above. B suffixed indicate at-or-below. For restrictions between to altitudes enter lower limit first, then upper limit, i.e. 100A120B.

Multiple element entries can be placed as a singly entry by separating fields with a slash. For instance, a cruise wind of 100 degrees at 75 kts would be entered via the scratchpad as 100/75.

To change single elements in multi-element values requires either a leading or trailing slash, depending on whether the data is on the left or the right of the CDU. To put it simply, include the slash as shown in the data field relative to the entry: XXX/ for items on the inner right side of the scree, while items on the inner left side prepend the slash - /8.0. Data closest to the LSK can be entered without slashes.

Elements close to LSK do not requires slashes, while elements further from the LSK require a slash in the appropriate position.

Specific keys

The functions keys give direct access to various CDU pages. An important one is the EXEC key, which executes any modification that has been entered into the CDU. A pending modification is indicated by a light bar above the EXEC key.

Key	Page	Includes
INIT REF	System initialisation and performance data menu	Position and performance
RTE	Route pages - page 1 includes origin and destination, as well as company routes	Other pages include route segments or direct routings
DEP ARR	Used to modify departure and arrival procedures
FIX	Displays fix page. Used to display and create fixes on current route
LEGS	Used to modify lateral and vertical nav data. Page is called MOD RTE when pending modification	Includes waypoints, speed and altitude at waypoint, RNP/ANP values
HOLD	Hold page. Holding procedures for missed approach are displayed here
PROG	Dynamic flight information data, waypoint and destination, ETA’s, fuel remaining	Wind data, RTA (required time of arrival), RNP data

Alert Messages

There are 4 alert messages on the sides of each CDU:

• MSG → Message displayed on scratchpad
• OFST → LNAV function is giving lateral offset routing
• CALL → Subsystem other than FMC requests control of CDU

How do you select VREF speeds on the FMC?::On the APPROACH REF page, which is accessed with the INIT REF key during flight. How do you enable pending modifications on the FMC?::If the light bar above EXEC is on, there is a pending modification. Press EXEC to execute said modification. As the aircraft reaches ToC, the FMC/CDU auto sequences from CLB page to CRZ page.::True FPA is the actual flight path angle based on present ground speed and ___ . :: Vertical speed. During a reduced thrust takeoff, the maximum reduction that the FMC will allow is ___ N1.::25% During a CLB-2 reduced thrust climb out, N1 is reduced by ___ .::6% Any page containing boxes indicates that data entry into that field is mandatory.::True.

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