Aoa 737ngx Fms Handout

Flight Management System20

www.flyaoamedia.com

sect

ion

Flight Management System www.flyaoamedia.comPage 20-1Rev 1.0 Jul 12

The material covered in this document is based off information obtained from the original manufacturers’ Pilot and Maintenance manuals. It is to be used

for simulation purposes only.

Copyright © 2012 by Angle of Attack Productions, LLCAll rights reserved


Table of Contents Table of IllustrationsFMC Overview 3FMC vs CDU 6Control Display Unit 7Inertial Reference System 10GPS 15

Figure 20-1. Flight Managment Computer 3Figure 20-2. Example LNAV Profile 4Figure 20-3. Example VNAV Profile 5Figure 20-4. Control Display Unit 9Figure 20-5. Air Data Inertial Reference Unit 11Figure 20-6. IRS Mode Selector: NAV Position 13


FMC OverviewDuring the Autoflight lesson you learned about the impressive amount of hardware working behind the scenes to make your control over the aircraft easier through autoflight methods.

Although there are many things that the autoflight system can do, none are as complex and efficient as those modes given to us by correct FMC, flight management computer.

The flight management computer is the pilots means of controlling the optimum flight profile for the aircraft. These two FMCs (figure 20-1), one each side, take the information for the flight that the pilots have entered and create the desired optimum flight path.

The FMC can then take that flight path, and through use of the autoflight system components we spoke about last lesson, will control the aircraft with the utmost precision.

The two modes directly impacted by the FMC are the LNAV and VNAV modes.

● LNAV (Figure 20-2) is our lateral navigation, or navigation from point-to-point. This part of the flight management computer takes the route entered by the pilots and sends that information to essentially steer the aircraft

THIS UNIT CONTAINSELECTROSTATIC DISCHARGESENSITIVE ITEMS IDENTIFIED

WITH YELLOW MARKING

CAUTION

PWRON

FMCVALID

SI MODIFICATIONS

SI SMITHS INDUSTRIES

Figure 20-1. Flight Managment Computer

João Marcelo

Realce

João Marcelo

Realce

João Marcelo

Realce

João Marcelo

Realce


along a desired path. Of course, the process is much more complicated than this simple explanation. But this will suffice for the moment.

● VNAV (Figure 20-3) is our vertical navigation, giving us climb performance calculations, optimum flight level cruise, and so on. Our Top of Climb (TOC), Top of Descent (TOD), and vertical path along the waypoints selected can also be maintained.

These two modes are selectable from the MCP. When selected, and if the information is correct and achievable in the FMC, the aircraft will precisely follow that path.

Worth mentioning at this point is that the LNAV and VNAV modes cannot take over all operation of the aircraft for all phases of flight. In other words, there will inevitably be times of transition where other modes from the MCP will need to be selected and followed. In the case of takeoff, manual control is used, as one of many examples.

In addition to what’s been discussed so far about LNAV and VNAV, the FMC is not a simple piece of equipment to operate. Of course, for a seasoned pilot it ’ll be a different story and makes sense to a certain extent.

FMC Overview (Cont.)

OO

YCF

MSS

Figure 20-2. Example LNAV Profile

João Marcelo

Realce

João Marcelo

Realce


However, there is an underlying change in how the aircraft is operated when we bring something like the FMC into the picture. This means that as a crew you’re no longer navigating VOR to VOR, or Fix to Fix. Rather, now you’re punching in numbers, route data, and other preferences to allow the Autoflight system as a whole to handle the best possible scenario and follow the desired path.

Keep in mind that the FMC is a very complex computer with a vast number of pages. It isn’t going to be as intuitive or straight forward as your smartphone or even a PC. Rather, it is a system designed even before the smartphone and large adoption of the PC to handle one specific purpose; fly the airplane with precise numbers. The implementation of the FMC allows crews to manage flights more efficiently in the ever-growing complexity that comes with navigating all over the world.

At this stage in the training, much like we discussed in Autoflight, we will not be going over each and every page and feature of the FMC and how it interacts with the autoflight system. Rather, we will be teaching this along with the other autoflight modes and operations as we work through FlightWork and LineWork. In other words, let ’s learn this while in the air.

FMC Overview (Cont.)

35000

25000

10000

5000

15000

1000

0OO

YCF MSS

T/DT/C

Figure 20-3. Example VNAV Profile

João Marcelo

Realce


FMC vs CDuThere is a large misconception out there when speaking about the FMC. Technically speaking, the FMC is a computer that works in the background from anything seen in the cockpit. In other words, the pilots never see the FMC, just the data it helps display.

The real interaction with the FMC and display of it ’s data comes through the CDU, Control Display Unit. In other words, this is where the FMC is controlled and displayed. The CDU is very often confused for the FMC. Many people will refer to the CDU as the FMC, which is incorrect. Here at Angle of Attack we have been guilty of this mixup in the past, and we’ll most likely make the same mistake again.

To put it in simple terms, the CDU is not the FMC, and calling it the FMC is incorrect. However, we won’t hold it against you. Everyone will still understand what you’re referring to.

Notes

João Marcelo

Realce

João Marcelo

Realce

João Marcelo

Realce


itself from that line. Obviously this would be based on the page we’re using and what is required. You’ll see later just how simple that process is.

Worth mentioning while we’re on the display is the scratchpad. In this area we will enter information from the keys below, or copied from the line select keys, where we can then place it where desired, again, with the line select keys. A bit of a jumble as it ’s said, but this will make sense later as we are transferring data around.

Now we move down to the Function Keys. Each one of the keys represents a particular area of the CDU where we can get into specific modes easily and quickly. Although there are often prompts in other ways, this is a quick way of navigation from one section to another. You can imagine that when you’re in the air and things are busy, this kind of functionality is essential.

You’ll become quite familiar with each and every section of the CDU, so you’ll know as well how to quickly get somewhere specific with it ’s corresponding Function Key.

Last but certainly not least are the AlphaNumeric keys located at the bottom of the CDU. There isn’t a lot that

Control Display unitThe CDU itself is a simple unit. We’ll now go over some of the minor details about some of the terminology related to the CDU and how things are laid out. (Figure 20-4).

The CDU itself is a fairly simple unit to control. Rather than the touchscreen interface so popular in today’s world, the CDU is more of a keyboard type interface.

Two CDUs are available for both the Captain and First Officer. You’ll be using the Captain’s CDU most of the time, however, operation of either CDU is exactly identical in operation and functionality.

We’ll now go through, top to bottom, and talk about the different physical attributes of the CDU.

First, you’ll notice the display which takes up a good amount of real estate. This display will show all the data necessary as communicated from the FMC through the Autoflight system.

On the left and right of the display are seen various keys called Line Select Keys (LSK). These are referenced as 1 left through 6 left, and 1 right through 6 right. They allow us to enter in selected information, or select the information


can be said about these keys outside of common sense. With these keys we enter information into the scratchpad, again, located at the bottom of the CDU display, where it can then be placed accordingly with line select keys.

Notes

Control Display unit (Cont.)


PREVPAGE

N1LIMIT FIX

LEGSMENU

INITREF RTE CRZ

HOLDINIT REF

DES

PROG EXEC

NEXTPAGE

CLB

A B C D E

F G H I J

K321

654

987

/0. + -

L M N O

P Q R S T

U V W X Y

Z SP DEL / CLR

FMC <REQ>

MENU

SETUPPMDG

ACARS

<

>

FS ACTIONS >

<

DFDAU<

LSK R1LSK L1

LSK R2LSK L2

LSK R3LSK L3

LSK R4LSK L4

LSK R5LSK L5

LSK R6

Alphanumeric Keys

LSK L6

Scratchpad

Function Keys

Figure 20-4. Control Display Unit


discuss that later.

Because these IRS systems were invented before the day of GPS data being available and reliable, it ’s not as simple as firing up the IRS to get current position and information.

Rather, the pilots have to go through what is called an alignment process to initialize the IRS. Otherwise, information will be unreliable and inaccurate.

This alignment process takes about 10 minutes. We will be going through this process many times in the training, including what is called a quick align that takes only 30 seconds.

However, even with a quick align, an initial full align is required.

The IRS is certainly not transparent like some of the other Autoflight components. In other words, we have some data that is displayed.

Present position and other data is displayed through the IRS Display Unit, located on the aft overhead panel.

Contrary to popular belief, the 737NGX does not magically know where it is at all times. Rather, that is thanks primarily to the Inertial Reference System or IRS.

The IRS, which actually consists of two IRS units, is a very complex combination of lasers and accelerometers that provide the autoflight system, including the FMC, with incredibly important information (Figure 20-5).

This includes: ● Attitude

● True and Magnetic Heading

● Acceleration

● Vertical Speed

● Ground Speed

● Track

● Present Position

● and Wind Data.

Although there are GPS units installed onboard most modern 737s, the IRS is the primary means of attitude and heading data on the aircraft. A GPS equipped 737 uses the GPS as the primary means of position data. We’ll

Inertial Reference System

João Marcelo

Realce

João Marcelo

Realce


PITCH RATELASER GYRO

ADIRU

LASER GYRO

DETAIL

LONGITUDINALAXIS

Y

Z

X

VERTICALAXIS

YAW RATELASER GYRO

ROLL RATELASER GYRO

IRPROCESSOR

IRDATAOUT

ACCELEROMETERS

LATERALAXIS

!

Figure 20-5. Air Data Inertial Reference Unit


Once a mode is selected with the knob, different status’ are then displayed above with the indicator lights. The process is straight forward. If there is anything amber or flashing, that means we’re being warned of a possible issue or the aircraft isn’t aligned. During perfect, aligned operation, everything should be extinguished.

In the OFF position, the mode selector does the following: ● All Alignment is lost in the respective IRS.

● All electrical power is removed from the system after a 30 second cool-down period.

In the ALIGN position, the following action takes place: ● Rotating from the OFF position to the ALIGN position

starts the alignment cycle.

● Rotating from the NAV position to the ALIGN position, aircraft position is automatically updated and groundspeed errors are zeroed out.

The NAV position, which is used most often, does the following:

● The system enters the NAV mode after alignment is completed.

● In Nav mode, all IRS information is available to other

● Latitude and longitude is displayed at the top of the display unit and can also be entered with the keys, bottom right.

● Selected with the display is a test mode, track and groundspeed, Present Position, Wind and Heading information modes. Also coupled with the heading information are any status messages for maintenance. These codes will be widely unrecognized by the pilots.

● Last, the pilot can select which IRS information to display, which is data from the left or right IRS.

Alignment, as mentioned before, is an initial process that has to be done. This process is for the most part automated, however, it does require some control through the IRS Mode Selector.

We’ll now go through the indications and some of the scenarios on the IRS Mode Selector (Figure 20-6), as we aren’t going to be spending a lot of time with it during FlightWork and LineWork.

Most integral to this system are the mode selector knobs themselves at the bottom. Both the left and right IRS need to be aligned and operating for data to be reliable.

Inertial Reference System (Cont.)


aircraft systems.

ATT mode has the following conditions: ● Only attitude and heading information is available, as

this is more of an emergency mode.

● Heading information is invalid and flagged until the magnetic heading is manually entered.

● The selector must be cycled OFF before it can be put into NAV or ALIGN.

You would think in normal circumstances that you’d go through a progression of OFF, to ALIGN, to NAV, to get the aircraft aligned in preflight. However, as you will see later, alignment still takes place if you switch the selector straight from OFF to NAV, which will be our means of aligning the system; a very common airline procedure in the 737.

Now let’s talk about a few of the light indications above to wrap up the IRS section.

First off is the light you’re going to see most, which is the ALIGN light.

Inertial Reference System (Cont.)

Figure 20-6. IRS Mode Selector: NAV Position

João Marcelo

Realce

João Marcelo

Realce


pulling from the hot battery bus rather than getting AC power, like under normal circumstances.

The DC FAIL light being illuminated means that the DC power to the IRS is not normal. Much like the ON DC light, when DC FAIL isn’t lit, everything is normal. And it also means it ’s running normally on AC power.

This does it for the IRS Mode Selector.

Finishing up our discussion on the IRS is the IRS Transfer Switch. Put simply, this switch allows for the flight instruments to get their information from one IRS or both. Normal operation, as noted below the switch, is both.

The IRS is an integral part of the overall navigation of the aircraft. And without it, the FMC wouldn’t have redundancy, and we wouldn’t have heading or attitude data.

Inertial Reference System (Cont.)When illuminated steady, the ALIGN light is currently aligning or if flashing there is an error and alignment isn’t possible. You will run into these situations, so it ’s important to know.

The ALIGN light is off when the system is aligned and operating correctly, but will only turn off if in NAV mode. The ALIGN light will also turn off when ATT mode is selected and both the heading and attitude information is available.

In a perfect situation, which is most often the case, we want to be in NAV mode, with the ALIGN light extinguished. This means we are operating normally and the IRS is sending all pertinent information to the various aircraft systems.

Moving on, the FAULT light is AMBER when a system fault is detected. These may be able to be fixed on the ground with a realignment, but usually a call would need to be made to maintenance about the details. The specific fault may show up as a code on the IRS Display Unit’s system display page.

The ON DC light will light up momentarily during alignment, but to have it lit up continually is abnormal as it is now


GPSOur final subject in this FMC lesson is the GPS, Global Positioning System. Many if not all of you are familiar with what a GPS is. However, we’ll go through a quick review of how the system works. In addition, we’ll discuss the 737NGX specific components and considerations.

A GPS system uses multiple satellites to triangulate position. Hundreds of these satellites located all around the globe can for the most part track, with an astounding degree of accuracy, position and now even altitude.

Although the 737NGX doesn’t get altitude data from the GPS, it can get very accurate GPS data with it ’s two GPS sensors. Not all 737’s are equipped with GPS as this is a company option. The majority of delivered 737’s these days have GPS units, however.

How does this relate to the FMC? The FMC uses GPS data as it ’s primary positioning information, while the IRS remains secondary. If the GPS data is unreliable or has an issue, the IRS is a quick backup. This makes for pin-point accuracy of the aircraft position, and has lead to RNP approaches and other incredibly useful advances in navigation. We’ll be talking a lot more about those throughout FlightWork, including where to see the indications.

Notes

João Marcelo

Realce

Documents

Aoa 737ngx Fms Handout