15.14 Ignition

Question 1

What do these stand for?
EGT
TIT
TGT
ITT
TOT

Answer 1

Exhaust gas temperature
Turbine inlet temperature
Turbine gas temperature
Inter stage turbine temperature
Turbine outlet temperature

Question 2

Where would you find the highest temperature on the engine?

And what is used to measure this?

Answer 2

Directly behind the combustion chamber where hot gas hits HP turbine (turbine inlet guide vanes)

TIT

Question 3

Where is the EGT measurement taken from?

Answer 3

Either between the HPLP turbine or directly behind the LP turbine

Question 4

What are all of the indications relative to?

Answer 4

The temperature of gases entering first stage turbine inlet guide vanes

Question 5

Where are thermocouples placed?

Answer 5

Turbine discharge as it’s impractical to measure at turbine IGV

Question 6

What does the EGT indicate?

And where are they located?

Answer 6

The average temperature measured by the individual thermocouples

Placed at intervals around perimeter of engine turbine casing or exhaust duct

Question 7

How is the EGT indicator sealed?

Answer 7

Hermetically sealed

Question 8

How does TIT operate?

And what happens if it reaches a predetermined limit?

Answer 8

By using duel thermocouple system that has two electrically independent junctions providing dual system reliability

And over temp warning light in the indicator illuminates

Question 10

What are the three groups engine thrust indications?

Answer 10

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

Question 11

What is the purpose of the primary indications?

Answer 11

To monitor performance and limits and sets thrust for flight phases

Question 12

What is the purpose of system indications? (Secondary)

Answer 12

To monitor operation of oil and fuel systems and to detect malfunctions quickly

Question 13

What can be used to give thrust indication?

Answer 13

Either N1 or EPR

Question 14

Under what conditions can warnings and cautions be displayed?

Answer 14

When indication exceeds a limit
Low oil pressure
Filter clogged
When an unlocked thrust reverser detected

Question 15

What is trend monitoring?

Answer 15

Used to detect early stages of problems
Done in a workshop by analysing engine data and recorded in flight deck by ACM

Question 16

What are the three analysis performed in trend monitoring?

Answer 16

Thermodynamic
Mechanic dynamic
Oil consumption

Question 17

How is the EPR displayed?

Answer 17

Actual EPR shown by pointer or digital valve
Amber or red line shows EPR for Max available thrust
Blue circle shows the EPR that corresponds to actual throttle position

Question 18

What are the two types of pressure transmitters?

Answer 18

Bourdon tube
Strain gauge

Question 20

How does the boarding tube pressure transmitter work?

Answer 20

Pressure media will enter the tube causing it to extend the helical sea shaped. Closed-end is attached to a movement that moves a needle as the helical extends

Question 21

What is the Borden tube made from?

Answer 21

Copper, brass, aluminium or nickel alloy (Monel)

Question 22

What is a strand gauge used to measure?

Answer 22

The resistance change when a material deformed undergoes strain

Question 23

What configuration does the strain gauge use? And what’s the principle?

Answer 23

Wheat stone bridge configuration where resistance changes as the length of active arms changes when under strain

Resistance causes output voltage to change, which is amplified and filtered before the data can be read and analysed

Question 24

What warnings will be given if oil temp exceeds its limits?

Answer 24

Both visual and audible warnings

Question 25

What two indications does fuel flow provide? And what is the unit of measurement?

Answer 25

Actual fuel flow to engine engines Fuel used since engine start KG, LBS, tons

Question 26

What do all fuel indications require to provide a measurement?

Answer 26

Fuel flow transmitter Which measure the force supplied by the flow of fuel (F = M x a)

Question 28

What is the principle behind synchronous mass flow?

Answer 28

Fuel mass turns a turbine against a spring and deflection angle is measured An impeller driven by an electric motor accelerate fuel flow Acceleration of the fuel is constant so massive fuel is proportional to turbine angle

Question 29

What is the principle behind motorless mass flow? And how is it measured?

Answer 29

The fuel itself generates acceleration The angle is measured between rotating drum and rotating impeller Mass of fuels proportional to an angle between drum and impeller Using two coins and four magnets 2 at drum and 2 at impeller

Question 30

What happens as magnetic reluctance as the air gap increases in a variable reluctance sensor?

Answer 30

Magnetic reluctance increases

Question 31

What does a variable reluctance sensor detect?

Answer 31

Changes in magnetic flux between a magnet and a ferromagnet target

Question 32

What is a tachometer?

Answer 32

Permanent magnet driven by a gearbox with a speed proportional to N2 rotor speed It also supplies power to the computer

Question 33

What are the three types of speed indications?

Answer 33

Display clock type scale Display with moving vertical bar Classical electromagnetic indicator

Question 34

What is the red line limit?

Answer 34

Max permitted rotor speed Exceeding the red line can cause severe engine damage from over speed

Question 35

Where are the two sensors usually located for accelerometer?

Answer 35

One located in compressor area near N1 Road A Shift and One located in turbine area (turbine frame)

Question 36

What are the two types of accelerometers?

Answer 36

Accelerometer - (electromagnet) Piezoelectric - crystal accelerometer

Question 37

What happens if N1 or N2 speed signal fails?

Answer 37

Rotor identification shows broadband (BB)

Question 38

When would we see white on black secondary engine display?

Answer 38

When vibration is equal to or more than 4.0

Question 39

How does an electrical torque meter operate?

Answer 39

Measures angular displacement relative to that on the driveshaft It is comprised of two concentric shafts

Question 40

How does a hydraulic torque meter operate?

Answer 40

Engine pressure metered through a valve with a helical gear that moves in response to applied torque Measured in lbs/ft or percentage horsepower

Question 41

What can the hydraulic torque meter also be used?

Answer 41

Set power settings

Question 42

What is a power assurance test? And when must this be carried out

Answer 42

Checks engine can accelerate from idle to given EPR value within a specific time, and back to idle within a specific time Carried out after maintenance or installing a new engine

Question 43

What are the first three steps in a power assurance test?

Answer 43

1- operate at idle for five minutes 2- identify Max EPR for the day 3- anti-ice and bleed air switches off for better acceleration

Question 44

What is the time permitted for the engine to reach the same EPR Max value in a para insurance test?

Answer 44

Seven seconds or less

Question 45

What must be done at the end of a power assurance test before shutting down?

Answer 45

Operate at minimum idle for 10 minutes to safely reduce temperature