ATA77 Engine Indicating Jet Aircraft Maintenance Fundamentals

ATA 77 Engine IndicatingBook No: JAMF ATA 77 ALL Lufthansa Lufthansa Base Issue: July 2000 For Training Purposes Only Lufthansa 1995 ã Technical Training GmbH Training Manual Fundamental

ATA 77 Engine Indicating

Book No: JAMF ATA 77 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

Beijing Ameco

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

ATA 77 ENGINE INDICATING

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INTRODUCTION TO ENGINE INDICATIONS

ENGINE INDICATION SYSTEMS

Engine indications are used to monitor the parameters of the engine and its

systems

The engine indications can be divided into 3 groups First, there are the

perfor-mance indications that are also named primary indications

Then there are the system indications that are also called secondary

indica-tions

The third group of indications is used for engine trend monitoring and usually

not shown in the cockpit

The performance indications are used to monitor the performance and the

lim-its of the engine and to set the thrust for the different flight phases

The system indications are used to monitor the operation of engine systems

such as the oil or fuel system They are also used to detect malfunctions

quickly

Engine trend monitoring is done on the ground to detect engine problems at an

early stage It uses engine parameters that are automatically recorded by the

aircraft condition monitoring system, (ACMS)

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ENGINE SYSTEMINDICATION

ENGINE TRENDMONITORINGACMS

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Figure 1 Engine Indication System

co nhung thong so khong dung

de dieu khien ma chi dung de quan sat tuoi tho cua engine.

Engine Indication Systems (contd.)

You can find engine indications such as the ones shown on this ECAM display

system They have a combination of gauge type analog displays and digital

readouts

There are also analog indications with moving vertical bars such as the ones

shown on this EICAS display

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ENGINE PERFORMANCE INDICATIONS

The indication which is always located at the top is used to monitor and set the

engine thrust

Because it is not possible to measure the thrust directly, there are 2 different

indications which give an equivalent value

This is either the rotational speed of the fan, called N1 or the engine pressure

ratio

The other performance indications are the engine rotor speed indications for

each rotor system This means that in addition to N1, there is N2 and, if

avail-able, also N3

There is also the exhaust gas temperature indication (EGT) and the fuel flow

indication

Data for the indications is gathered by specific sensors or probes The data is

usually electrically transmitted to the indicators

Sensors fitted to engines with a FADEC system will first transmit the data to

the FADEC system computer

The computer then sends the data to the indicators or display system and also

uses it to control the engine

ENGINE SYSTEM INDICATIONS

We use the secondary engine indications to monitor the correct operation of

engine systems These are also called engine system indications

The indications for the oil system monitor the oil quantity, the oil pressure and

the oil temperature

The engine vibration indication shows you any imbalance that occurs in the

rotating parts of the engine For example an imbalance can be generated by

damage to blades or bearings

The nacelle temperature increases for example when there is a leakage of hot

air in the engine nacelle

The indications on the EICAS generally give the same information as the

indi-cations on the ECAM, although they are shown in a different way

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Engine System Indication (contd.)

There are also warnings and cautions displayed on the ECAM / EICAS page

when an indication exceeds a limit, or when, as shown here, the system

de-tects a low oil pressure Or when a filter gets clogged as indicated here Or

when an unlocked thrust reverser is detected

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ENGINE TREND MONITORING

Modern engines are very reliable and economic, but the performance of the

engine modules decrease during their lifetime

To prevent larger performance reductions or even engine problems during

flight you need a monitoring tool that alerts us to a problem at an early stage

This tool is called engine trend monitoring

The engine trend monitoring is done in the workshop by analysing engine data

that is periodically recorded during flight by the aircraft condition monitoring

system

The ACMS provides this data on a printout from the cockpit printer and it can

also usually transmit the data via the ACARS datalink to the ground

The transmitted engine data is analysed by a computer system in order to find

any parameters that indicate a trend towards a limit

3 different analyses are usually done, the thermodynamic analysis, the

me-chanic dynamic analysis and the oil consumption analysis

The thermodynamic analysis checks the pressures and temperatures along the

gas flow path It also monitors the feedback signals from the VSV and VBV, the

active clearance control and the fuel flow

The data gives exact information about the condition of the engine components

involved in the thermodynamic process

The mechanic dynamic analysis mainly checks for failures of the rotor system

For example imbalances and bearing failures To do this it checks engine

vibra-tion and rotor speed signals

The oil consumption analysis generates an alert when the oil consumption

ex-ceeds a certain level

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VBV VSV FUELFLOW ACC

ROTOR SPEED INDICATION

INTRODUCTION

In all engines there is a rotor speed indication for each individual rotor system

There is an N1 indication for the low pressure rotor and an N2 for the high

pressure rotor There is also an N3 indication if the engine has 3 rotors The

engine rotor speed indications are always expressed as a percentage of a

100% design speed Now read the N1 value for engine number 2 in the

exam-ple

Each rotor speed indication has 3 main parts:

: the sensor

: the data transmission

: and the indication

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TACHOMETER GENERATOR

There are 2 different types of sensor which can measure rotor speed on

en-gines One is the variable reluctance type sensor The other is the tachometer

generator type which is usually located on the gearbox

The tachometer generator has a permanent magnet that is driven by the

gear-box with a speed that is proportional to the N2 rotor speed The rotating

mag-netic field generates a 3 phase AC voltage with a frequency that is proportional

to the input speed The frequency is converted/changed (transferred) back to

the speed signal in either a computer or indicator

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Figure 7 Tachometer Generator

do vong quay; gan 1 cai

tachometer de do ti le vong

quay cua N2

Tachometer Generator (contd.)

In older generation aircraft there are rotor speed indicators which are driven

directly by the voltage from the tachometer generator The indicator has a

syn-chronous AC motor that generates a speed proportional to the input frequency

which is the same as the speed of the drive shaft on the tachometer generator

An eddy current clutch transfers the speed into a proportional torque which

moves the gauge pointer to the correct indication

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SYNCHRONOUSMOTOR

Tachometer Generator (contd.)

In modern aircraft systems the tachometer generator sends the 3 phase AC

voltage to the FADEC computer where it is used to calculate the speed signal

The tachometer generator also supplies electrical power to the computer and is

therefore also called dedicated generator or control alternator In the next

seg-ment you are going to learn about the other speed sensor type

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POWERSUPPLY+

VARIABLE RELUCTANCE SPEED SENSOR

Now let us have a look at the variable reluctance speed sensor which is

nor-mally used to measure the N1 rotor speed Can you identify the N1 sensor on

the graphic? The variable reluctance sensor is positioned directly in line with

the phonic wheel on the compressor shaft As you can see phonic wheels have

different shapes, but this is not important The important thing is that the

rotat-ing phonic wheel alternates metal and air at the tip of the sensor to change the

sensor’s magnetic field.) Because the sensor must be located near the

com-pressor shaft it often needs a long support tube to make replacement of the

sensor possible You must be very careful during replacement not to bend or

damage the probe

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Figure 10 Sensor and Phonic Wheel

cach 2: co 1 speed sensor de do toc do vong quay thong qua cac banh rang (dem so rang)

Variable Reluctance Type Sensor (contd.)

There are similar sensor types located near the fan blades on some engines

The fan blades are used instead of a phonic wheel to change the magnetic field

of the sensor You can find There is also a variable reluctance type sensor on

the gearbox which measures the N2 rotor speed In this installation a gear in

the gear box has the function of the phonic wheel In all applications a

com-puter is used to calculate the rotational speed from the sensor pulses The next

segment looks at rotor speed indications

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There are 3 different types of rotor speed indication A display with a clock type

scale, a display with a moving vertical bar and the classical electromechanical

indicator All 3 indications show the actual N1 value with an analog and a digital

indication There is always a speed limit indication which is usually a red line

This is the maximum permitted rotor speed

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Indications (contd.)

When actual N1 exceeds the red limit it can damage the engine To make this

dangerous situation clear to the pilot the indications on the displays change to

red accompanied by warnings from the central warning system The maximum

exceedance value is recorded and in modern aircraft it also initiates an

excee-dance report from the engine trend monitoring This is used for planning the

necessary maintenance actions

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Indications (contd.)

When N1 decreases below the red limit a red exceedance pointer shows the

recorded maximum exceedance value Or you just get a red box around the

digital readout to show that an exceedance occurred You can read the value

with the CMC You can reset the exceedance value when you finish the

neces-sary maintenance actions any ground maintenance that is necesneces-sary You can

reset the exceedance indication by pressing the corresponding pushbutton in

the cockpit In modern aircraft this is done automatically with the next engine

REDBOX

Indications (contd.)

When the N1 indication is used to set engine power, then an additional

indica-tion is needed to show the pilot the N1 value for the required thrust This value

is called N1 limit or N1 command or reference N1 Find the N1 limit indication

The N1 limit or N1 command shows the N1 that is required for a specific flight

phase such as take off or climb The value is calculated by the flight

manage-ment or autothrottle system There is always an analog indication on the scale

and an additional digital readout You can also set this value manually with the

knob on the lower indicator For the displays, you set the value via the flight

management system There is more detail on this in the avionic course On

some displays you also can find an amber line that shows the N1 for the

maxi-mum available thrust and a blue circle or white line that shows the N1 for the

actual throttle position

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EPR INDICATION

INTRODUCTION

You only find an EPR indication on some aircraft/engine combinations It is

al-ways located at the top of the engine indications, because it is used to set the

engine power The EPR corresponds to the engine thrust because it is the ratio

of the total pressure at the turbine outlet to the total pressure at the fan inlet

Other engine types do not need an EPR indication because the power is set

with the N1 indication Each EPR indication system has 3 main parts: 2

pres-sure pickups that are connected by tubes with a computer, a computer which is

either a separate EPR transmitter or part of the FADEC computer and the

indi-cator, which is located in the cockpit

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PRESSURE SENSOR

To calculate and indicate the EPR you must measure 2 pressures The

pres-sure is given the name of the station that detects it For example the P2 and

the P5 pressure P2 is the total air pressure at the fan inlet It is measured by a

pressure probe which is located in the fan airstream Like other air data probes

it is electrically heated to prevent icing P5 is the total gas pressure at the

tur-bine exit This pressure is also sensed by probes or like in this example with

small holes in 3 of the turbine frame struts The individual pressures are

col-lected by pickups in the turbine frame and guided by tubes to a common

pres-sure manifold This gives an average P5 prespres-sure value The 2 prespres-sure values

are passed to the computer for it to calculate the pressure ratio Shown here is

an EPR transmitter, which is an earlier type of computer Before the calculation

can occur, the computer must change the pressure into a proportional electrical

signal The EPR transmitter use electromechanical pressure transducers with,

for example, bourdon tubes

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Pressure Sensor (contd.)

On modern engines the EPR calculation is done in the FADEC computer It

uses electronic pressure transducers like in the air data system These

trans-ducers are much smaller, more reliable and more exact than the

In this segment we will show you 2 different types of EPR indication Firstly the

indication on a display unit which you find on modern aircraft and secondly a

classical electromechanical indicatior on older generation aircraft You may

have noticed that the actual EPR indication is shown by an analog readout and

a digital value The EPR command has the same function as the N1 command

that you learned in lesson 2 This example shows the EPR required for a

flex-ible takeoff On the classical indicator this value is called the EPR limit which is

also shown in both analog and digital format You can also set the value

manu-ally by pulling the knob On the display you can find also 2 indications you have

already seen on the N1 indicator This is the amber line that shows the EPR for

the maximum available thrust and a white circle that shows the EPR that

corre-sponds to the actual throttle position

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