15.14 Engine Indication Systems

Question 1

Where are the highest internal engine temperatures?

Answer 1

At the Turbine Inlet (TIT) directly behind the combustion chamber

Question 2

Where is EGT measured?

Answer 2

Downstream of the combustion chamber where its cooler.

Question 3

What are EGT temepratures?

Answer 3

600c to 900c

Question 4

What is used to capture engine temperature data?

Answer 4

Thermocouples around the exhaust duct

Question 5

Why is EGT monitoring important on a turbine engine?

Answer 5

Helps prevent thermal damage and indicates when temperature limits are exceeded

Question 6

Why is EGT used instead of TIT for regular measurement?

Answer 6

TIT is too hot to measure directly so EGT measured downstream

Question 7

What components are found in a TIT indicator system?

Answer 7

Chopper circuit, two phase motor, feedback potentiometer, amplifier and over- temp warning light

Question 8

What are dual thermocouples used for?

Answer 8

One set sends signals to the flight deck
Other to engine monitoring/ control systems

Question 9

What are the key features of digital temperature indicators?

Answer 9

They don’t use resistance-type indicators and provide clear flight deck data.

Question 10

What is the function of the chopper circuit?

Answer 10

Converts signals from thermocouples DC to AC for the motor

Question 11

Whats the function of the two phase motor?

Answer 11

Moves the needle to indicate the temp

Question 12

Whats the function of the amplifier?

Answer 12

Boosts the thermocouple signal

Question 13

What happens if TIT exceeds limit?

Answer 13

Overtemp light

Question 14

Whats the function of the potentiometer?

Answer 14

Works with the motor to ensure the needle is in the correct position

Question 15

What are three groups of engine indications?

Answer 15

• Performance indications (primary)
• System indications (secondary)
• Engine trend monitoring

Question 16

What are performance indications used for?

Answer 16

To monitor engine performance, set thrust for different flight phases and ensure limits are not exceeded

Question 17

What do system indications monitor?

Answer 17

Engine systems like oil and fuel systems to detect malfunctions early

Question 18

Whats engine trend monitoring?

Answer 18

Ground based analysis of engine parameters to detect early signs of deterioration using ACMS

Question 19

What are the primary thrust indications for turbojet engines?

Answer 19

N1 (fan speed)
EPR (Engine pressure ratio)

Question 20

What are N2 and N3 in engine indications?

Answer 20

Rotor speed indicators for additional engine shafts beyond N1.

Question 21

What other performance indicators are shown alongside N1 and EPR?

Answer 21

EGT (Exhaust Gas Temperature) and fuel flow.

Question 22

What does EPR measure?

Answer 22

Ratio of turbine exhaust pressure to engine inlet pressure
indicates thrust output

Question 23

How is EPR calculated?

Answer 23

Using pressure probes in the engine inlet and turbine exhaust

Question 24

How is EPR displayed to the crew?

Answer 24

Analogue and/or digital indicators showing actual thrust, with lines showing maximum thrust and throttle position.

Question 25

What is a FLEX take-off?

Answer 25

A thrust reduction method using an assumed higher outside air temperature to reduce engine wear.

Question 26

What do thermodynamic, mechanical-dynamic, and oil consumption analyses monitor in engine trend monitoring?

Answer 26

Gas flow temperatures/pressures, rotor system faults, and excessive oil use, respectively.

Question 27

What alerts are shown on ECAM/EICAS for system issues?

Answer 27

Low oil pressure, filter clogging, and thrust reverser faults.

Question 28

Why is monitoring oil pressure important in a turbine engine?

Answer 28

To prevent engine failure due to inadequate lubrication and cooling.

Question 29

What does the oil pressure indicator usually show?

Answer 29

The discharge pressure from the engine oil pump.

Question 30

What are the two main types of oil pressure transmitters?

Answer 30

Bourdon tube type and strain gauge type.

Question 31

How does a Bourdon tube transmitter work?

Answer 31

Pressure deforms the tube, moving the needle or sending a signal via a potentiometer.

Question 32

What materials are commonly used to make Bourdon tubes?

Answer 32

Copper, brass, aluminium or nickel alloy like monel

Question 33

How does a strain gauge measure pressure?

Answer 33

Detects strain induced resistance changes and outputs a proportional voltage

Question 34

What is a wheatstone bridge used for in a strain gauge?

Answer 34

To detect small resistance changes and produce a measurable voltage signal

Question 35

What is the function of the low oil pressure switch?

Answer 35

To trigger a warning if oil pressure drops below safe limits.

Question 36

When does the low oil pressure switch close the circuit?

Answer 36

When oil pressure is too low to keep the contacts open.

Question 37

What does the oil temperature indicator measure?

Answer 37

The temperature of oil entering the oil pressure pump.

Question 38

What sensors are commonly used for oil temperature measurement?

Answer 38

Resistance Temperature Detector (RTD) and Thermocouple.

Question 39

What happens when oil temperature exceeds safe limits?

Answer 39

A warning light or audible alert is triggered to warn the flight crew.

Question 40

What does engine vibration indication help detect?

Answer 40

It helps identify rotor imbalance, which may be the first sign of engine damage.

Question 41

What are the main components of the engine vibration monitoring system?

Answer 41

Vibration indicators in the flight deck, vibration sensors (accelerometers), and the Engine Vibration Monitoring Unit (EVMU).

Question 42

What do vibration sensors measure and how?

Answer 42

They measure radial acceleration of the rotor using accelerometers.

Question 43

Where are vibration sensors typically located?

Answer 43

One near the N1 shaft (compressor) and one on the turbine frame.

Question 44

What are the two main types of vibration sensors?

Answer 44

: Electromagnetic and piezoelectric-crystal sensors.

Question 45

How does an electromagnetic sensor work?

Answer 45

A moving coil vibrates in a fixed magnetic field, generating AC voltage from relative motion.

Question 46

How does a piezoelectric sensor work?

Answer 46

Vibration causes an inertia mass to compress a crystal, generating voltage.

Question 47

What happens on the display when vibration exceeds 4.0 units?

Answer 47

Vibration data appears on the secondary display and is shown in reverse video.

Question 48

What is the purpose of an Engine Balancing System?

Answer 48

It calculates the required balance weights to reduce vibration to acceptable levels.

Question 49

Why is torque measured in turboshaft engines?

Answer 49

Because turbine gas temperature and RPM alone can't accurately indicate power output.

Question 50

What are the two main types of torque meters?

Answer 50

Electrical and hydraulic.

Question 51

What does an electrical torque meter consist of?

Answer 51

: A torque meter assembly, a phase detector, and an indicator.

Question 52

How does an electrical torque meter work?

Answer 52

It detects the twist between two concentric shafts using toothed gear wheels and magnetic pickups to create a phase difference signal.

Question 53

What causes the twist in the electrical torque meter shaft?

Answer 53

Torque applied to the drive shaft connecting the engine to the gearbox.

Question 54

What does a phase comparator do in a torque meter system?

Answer 54

It compares signals from the pick-up coils and sends a signal to the torque indicator.

Question 55

How does a hydraulic torque meter work?

Answer 55

Torque moves a helical ring gear that adjusts oil pressure through a valve system, making oil pressure proportional to applied torque.

Question 56

Why must a torque meter be calibrated?

Answer 56

To ensure its accuracy, especially since it's used for setting power settings.

Question 57

Whats the purpose of a power assurance test?

Answer 57

To confirm the engine can accelerate and decelerate between idle and a specific EPR within required time limits after maintenance or installation.

Question 58

When should the power assurance test be performed?

Answer 58

After engine maintenance or installation, and only with reference to the engine manufacturer's manual.

Question 59

What safety precautions must be taken before running the test?

Answer 59

Park in an engine run-up area, point the aircraft into the wind, and chock the wheels front and back.

Question 60

How long should the engine idle before starting the power assurance test?

Answer 60

5 mins

Question 61

Why must engine anti-ice and bleed air switches be set to off during a power assurance test?

Answer 61

To ensure accurate engine acceleration performance during the test.

Question 62

How is the correct thrust setting marked during a power assurance test?

Answer 62

Slowly increase to max EPR over 30 seconds, then mark the thrust lever quadrant when stable.

Question 63

What are the acceptable acceleration and deceleration times?

Answer 63

Accelerate to max EPR within 7 seconds; decelerate to idle within 8 seconds.

Question 64

What must be done after operating the engine above 70% N1?

Answer 64

Idle the engine for 10 minutes to reduce temperature before shutdown.