ATA76 Engine Controls Jet Aircraft Maintenance Fundamentals

The forward thrust lever is used to control the thrust of an engine between idle and take--off thrust.. The master switches on the engine start panel are used to control the engine start

ATA 76 Engine Controls

Book No: JAMF ATA 76 ALL

Lufthansa Lufthansa Base

Issue: July 2000 For Training Purposes Only Lufthansa 1995 ã

Technical Training GmbH

Training Manual Fundamentals

JAR-66

Jet Aircraft Maintenance Fundamentals

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Aviation College

For training purpose and internal use only.

Copyright by Lufthansa Technical Training GmbH All rights reserved No parts of this training

manual may be sold or reproduced in any form without permission of:

Lufthansa Technical Training GmbH Lufthansa Base Frankfurt

D-60546 Frankfurt/Main

Tel +49 69 / 696 41 78

Fax +49 69 / 696 63 84

Lufthansa Base Hamburg

Weg beim Jäger 193

D-22335 Hamburg

Tel +49 40 / 5070 24 13

Fax +49 40 / 5070 47 46

Aviation College

ENGINE START CONTROLS

INTRODUCTION TO ENGINE CONTROLS

The main engine controls are the engine start controls, the forward

thrust controls and the reverse thrust controls

The start lever is used to switch fuel on and off and to switch ignition on during

engine start

The forward thrust lever is used to control the thrust of an engine between idle

and take off thrust The lever informs the fuel control unit how much thrust is

requested by the pilot

The third engine control is the reverse thrust lever

When the reverse thrust lever is activated the deflector doors are deployed and

the airflow is deflected to give reverse thrust

When the reverse thrust lever is pushed down the deflector doors move to the

stowed position and the engine delivers forward thrust

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FORWARD THRUSTLEVER

STARTLEVER

THRUST CONTROL SIGNAL

Introduction to Engine Controls

You can find similar engine controls on modern aircraft like this Airbus 320

The master switches on the engine start panel are used to control the engine

start sequence, the control levers help to set the required thrust and the

reverse latching levers are used with the control levers to give reverse thrust

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REVERSELATCHING LE-VER

REVERSE CONTROL SIGNAL

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TLA : thrust level angle

START CONTROLS OVERVIEW

The last segment that the ignition and the fuel supply to the combustion

chamber are switched on by the engine start lever

The fuel is supplied via a high pressure fuel shut off valve and a low pressure

fuel shut off valve

The low pressure fuel shut off valve is usually an electric motor driven valve

The position of this valve is indicated by the fuel valve closed light This light

illuminates when the valve is closed and goes out when the valve is open

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HP FUEL VALVE CONTROL

On this aircraft the high pressure fuel shut off valve is mechanically controlled

The HP valve opens when the engine start lever is moved up and closes when

the lever is moved down

The position of the HP fuel shut off valve is indicated by the position of the

engine start lever

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ELECTRICAL START CONTROLS

On some aircraft, for example the Airbus A320, the LP fuel valve position is

indicated on the ECAM display

It is controlled by the engine master switch

The HP fuel valve is not indicated directly but you know when it is open by the

fuel flow indication, the increase in the exhaust gas temperature or, by the fuel

LP FUEL VALVE CONTROL

The low pressure fuel shut off valve on modern Airbus aircraft is controlled by

the engine master switch

You may remember from the Fire Protection lessons that this valve is also

called the fire shut off valve and therefore it is also controlled by the engine fire

switch

When you operate the fire switch the fire relay opens and the low pressure fuel

shut off valve closes

The amber colour of the valve symbol on the ECAM display indicates an

emergency closure of the valve

The engine fire switch always has priority over the engine master switch

This applies on all aircraft with electrically controlled low pressure fuel shut off

valves

Mechanically controlled low pressure fuel shut off valves are only found on

very old aircraft They are not described in this lesson

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LP FUELVALVE

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khi keo can cuu hoa thi` lap tuc dong cac valve chua dau lai

va tat dong co. For Evaluation Only Copyright(C) by Foxit Software Company,2005-2008 Edited by Foxit Reader

MECHANICAL HP FUEL VALVE CONTROL

The controls for mechanical high pressure fuel shut off valves are routed from

the cockpit below the cabin floor to the center section and then via the wing

leading edges and the pylons to the fuel control units

The engine start lever has detents to secure it in the idle and cut off positions

Inputs from the lever are transmitted via rods, pulleys and cables to the start

drum in the pylon

The start drum is connected to the fuel control unit via a long push pull cable

Mechanically controlled high pressure fuel shut off valves are usually found on

older aircraft types Mechanical controls are more reliable than electrical

controls but they are heavier and they usually require more adjustments

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TO GINE

EN-PUSH-PULLCABLE

DISADVANTAGE

HPFUELVALVE

ADVANTAGE

STARTDRUM

STARTDRUM

ELECTRICAL HP FUEL VALVE CONTROL

Electrical high pressure fuel shut off valves are normally found on modern

aircraft engines They are located behind the fuel metering valve in the fuel

control unit They can be motor controlled or solenoid controlled, but they have

similar construction

Here you can see a more detailed view of the high pressure fuel shut off valve

in the fuel control unit

The valve assembly has two main parts the electrical component which

controls the servo valve and a spring loaded shut off valve which is connected

to the servo valve The spring loaded valve is usually called the pressurizing

valve

The high pressure fuel flows across the partially open fuel metering valve and

then through the servo valve to the aft side of the pressurizing valve The high

pressure fuel and the spring force keeps the pressurizing valve in the closed

position if the start lever is at cut off

This example shows a HP valve with a standard single coil solenoid Note that

the solenoid is energized when the HP shut off valve is closed

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Electrical hp fuel valve control cont.

When the start lever is moved to idle the solenoid is de energized and the

servo valve moves down

The pressure on the aft side of the pressurizing valve escapes into the case of

the fuel control unit

The pressure from the high pressure fuel pump pushes the pressurizing valve

open and the fuel can flow to the fuel nozzles

When the start lever is moved to the cut off position the solenoid is energized

and the servo valve moves up

This allows the fuel pressure to enter the aft side of the pressurizing valve

piston The piston closes and the supply to the fuel nozzles is cut off

The critical disadvantage of this single coil solenoid control system is that if the

electrical signal is lost the high pressure fuel shut off valve cannot be closed

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Electrical hp fuel valve control cont.

Other aircraft have dual coil solenoids at the HP valve as you can see here

These solenoids need electrical power to close the valve and to open the valve

The danger is that the valve can move to the closed position if there’s a short

circuit because of a damaged wire even if the start lever is in idle

Aircraft manufacturers have added protection circuits to prevent this dangerous

situation

These protection circuits differ from aircraft to aircraft Here you see a

simplified example where the pressurizing valve is equipped with a limit switch

The limit switch is activated by the plunger of the pressurizing valve

When the start lever is moved to idle the open coil of the dual solenoid is

energized and the servo valve moves down

This moves the pressurizing valve up and the plunger activates the limit switch

The limit switch de energizes the protection relay and this disconnects the

electrical power from the solenoid

This makes sure that the valve cannot move by mistake

Remember that this is a simplified example On many aircraft the power supply

and the ground are disconnected from the electrical control element

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MECHANICAL THRUST CONTROLS

INTRODUCTION

The mechanical thrust control system transmits the thrust lever input signals to

the fuel control unit on the engine The forward thrust levers are also called the

throttles They are located on the center pedestal There is one thrust lever for

each engine

The main positions of the forward thrust levers are idle and take off thrust

The reverse thrust levers are located at the top of the forward thrust levers

The main positions of the reverse thrust levers are reverse idle and full reverse

thrust

Forward thrust and reverse thrust use the same components

At the drum below the trust levers the forward thrust lever rotates the drum

counter clockwise and the reverse thrust lever rotates the drum clockwise

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REVERSE

THRUST

LEVER

FORWARDTHRUSTLEVER

CENTER PEDESTRAL

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FORWARD THRUST CONTROLS

The thrust control system is used to accelerate and decelerate the engine It

can not be used to shut down the engine

The thrust control system transmits the thrust lever signal to the fuel control

unit via control rods cables drums and pulleys and flexible controls such as

push pull cables

Here you can see a simplified schematic of a crank lever transmission

A power lever transmits the thrust lever signal to the fuel control unit When the

thrust control levers are in idle the power lever is in the mid position

If you move the thrust control levers forward the power lever moves up

If you move the thrust control levers to idle the power lever moves to the mid

RODDRUM

THRUSTLEVER

POWERLEVER

Forward thrust controls cont.

Some aircraft use racks and pinions in the transmission instead of crank levers

Racks and pinions are found at the thrust control drum at the engine pylon and

at the fuel control unit

The linear movement of the rack is transformed into a circular movement by

FUELCONTROLUNIT

Forward thrust controls cont.

A friction brake makes internal friction to keep the throttle control system in a

selected position The friction must be strong enough to prevent the throttles

moving because of vibration but it must be small enough to move the throttles

easily The friction brake can be a separate component as you can see on the

video or it can be an integral part of the autothrottle servo mechanism The

friction brake can usually be adjusted

The autothrottle servo mechanism receives signals from the autothrottle

computer and uses an electrical servo motor to move the thrust lever and the

mechanical transmission components and therefore change the power setting

for the engine

A coupling unit or an integral friction brake makes sure that the autothrottle

servo motor can be disconnected from the mechanical control system

A set of microswitches below the center pedestal are activated by the thrust

control levers

These switches are used for warnings and controls which depend on the lever

position for example take off warning, cabin pressurization and thrust

SEVO MOTORFRICTION BRAKE

CONTROLCABLES

AUTOTHROTTLESERVO MECHANISM(WITH FRICTIONBRAKE)

AUTOTHROTTLE SERVO MECHANISM

FROM AUTOTHROTTLECOMPUTER

FORWARD THRUST CONTROLS - ADJUSTMENT

All mechanical control systems must be adjusted to operate properly The

adjustment of the engine thrust control systems is usually split in two parts

The controls between the cockpit and the pylon are adjusted in one procedure

and the controls between the pylon and the fuel control unit are adjusted

seperately

The splitting point is usually the thrust control drum at the engine pylon

The adjustment between the cockpit and the pylon is usually done with the

thrust levers in idle and the adjustment between the pylon and the fuel control

unit is usually done with the thrust levers in a defined part power position

You can find the rig points where the transmission changes from one method to

another for example from control rods to cables as

Note that a travel check is necessary after adjustment of the thrust control

system This is to make sure that the thrust control levers can be moved over

the full range between idle and full forward thrust and between idle and full

reverse thrust The travel check is also to make sure that all rig pins are

RIGGINGPIN

RIGGINGPIN

RIGGINGPIN

RIGGINGPIN

REVERSE THRUST CONTROLS INTRODUCITON

The reverse thrust controls have three tasks to activate the thrust reverser to

increase engine power and to block the reverse thrust lever while the reverser

moves from the stowed to the deployed position

The reverse thrust control system uses the same mechanical control

components as the forward thrust control system In addition it has

microswitches below the center pedestal to activate the thrust reversers The

system also has a mechanical linkage, known as the throttle interlock system,

to prevent the pilot from increasing engine power until the reverser is fully

deployed

The reverse thrust control lever has three main positions one for each task

The normal position is used to stow the reverser the reverse idle position is

used to activate the reverser Here the lever is blocked by the throttle interlock

The full reverse throttle position is used to increase engine power

The throttle interlock system is the main difference between the reverse thrust

control system and the forward thrust control system

It is usually installed on the engine pylon and controlled by a mechanical

feedback system This feedback system is connected to the thrust control

system and the thrust reverser

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REVERSERFEEDBACKCABLE LH

REVERSERFEEDBACKCABLE RH

MICROSWITCHUNIT

REVERSER

IDLE

FULL REVERSERTHROTTLE

THROTTLE INTERLOCK - OPERATION

The throttle interlock system locks the mechanical control system while the

thrust reverser is moving from the stowed to the deployed position This

prevents damage to the reverser system and makes sure that the reverser is

fully deployed and latched before reverse power can be applied

On this example of a Boeing 737 thrust control system the mechanical interlock

linkage is located in the strut drum control box where the thrust control cables

and the reverser feedback cables are connected

When you look inside the strut drum control box you can see the thrust control

drum the thrust control rack with the thrust push pull cable and the pinion with

TO ENGINE FUELCONTROL UNIT

THRUST REVERSERFEEDBACK PUSH-PULL

CABLES

STRUT DRUMCONTROL BOX

THRUSTCONTROLDRUM

throttle interlock - operation cont.

When the reverse thrust control lever is moved to reverse idle the thrust control

pinion rotates counter clockwise until the lower roller contacts the cam of the

reverser feedback cam No further movement is possible but the reverser is

activated by the micro switch below the control levers in the cockpit

When the reverser deploys the reverse feedback mechanism rotates the

reverser feedback cam clockwise

When the reverser is fully deployed the contact surface of the feedback cam

doesn’t block the roller of the thrust control pinion any more

This allows you to pull the reverse thrust control lever to get full reverse power

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