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Module 15 > 15.21 > Flashcards

15.21 Flashcards

1
Q

When would maintenance personnel have to operate a gas turbine engine?

A

Confirming a flight crew reported fault
Post-maintenance basic engine or aircraft system checkout
Deterioration of engine performance
Aircraft control linkage wear
Moving an aircraft from one maintenance location to another
To taxi-check an aircraft system

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2
Q

How many thrust levers are there?

A

1 for each engine

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3
Q

What has to happen before the thrust reversers can be deployed?

A

Throttles must be in idle

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4
Q

What 2 things must you do before any engine start?

A

Confirm there is free movement of the engine
Clear area of FOD

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5
Q

What must be checked before positioning the aircraft?

A

The aircraft technical logbook for any outstanding entries that would prevent aircraft being moved or started

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6
Q

What must be ensured before positioning an aircraft for an engine run?

A

Undercarriage is down and locked
Oil levels are satisfactory, all panels secure
Sufficient fuel for ground run
Clear of FOD

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7
Q

How must the aircraft be positioned when doing a ground run?

A

Aircraft positioned into wind
Chocks fitted
Brakes applied
Ensure clear of buildings and other aircraft up to a 10 meters in front

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8
Q

Why would a fire service possibly be required?

A

If ground running with cowling open or carrying out a pressure engine run

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9
Q

When engines are running, what can be done if required?

A

Engine trimming

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10
Q

What shortens an engines operational life?

A

The more the engine is heated up and cooled down (do not increase above idle more than absolutely necessary)

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11
Q

Why are both engines run together?

A

To prevent an asymmetry problems when engines are running (one is more powerful than the other)

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12
Q

What must the oldest engine be used as when carrying out an acceleration check?

A

To use as a datum engine (reference)

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13
Q

What is done before cutting fuel off an engine?

A

The throttle levers are moved to idle

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14
Q

How long should you leave the engine to cool at idle before shutting down and why?

A

5 minutes to prevent possible seizure of the rotors

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15
Q

What are the 4 types of indications for engine monitoring?

A

Engine Pressure Ratio (EPR)
Rotor speed, N1, N2, N3
Fuel Flow (FF)
Exhaust Gas Temperature (EGT)

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16
Q

How do we measure EPR?

A

The ratio of the jet pipe pressure to the compressor inlet pressure is measured, giving an indication of thrust output

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17
Q

What does the N1 indication show?

A

The rotor speed of the low-pressure spool

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18
Q

What does the N2 indication show?

A

The high-pressure spool limit and speed switching during the engine start

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19
Q

What is FF used to monitor?

A

Fuel consumption during flight and for trend monitoring purposes

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20
Q

What is EGT used to recognise and prevent?

A

Overheating

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21
Q

How do centrifugal compressor engines measure engine power?

A

By comparing the relationship between engine RPM and Jet Pipe Temperature (JPT)

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22
Q

Why can’t axial flow bypass engines use the same method as centrifugal?

A

As there is no direct relationship between engine RPM and thrust

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23
Q

How to they measure engine power in an axial flow engine?

A

Compare static ambient pressure and exhaust gas pressure

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24
Q

What do torque monitoring systems indicate?

A

Indicate the power developed by a turbo-prop or turbo-shaft engines

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25
Q

What are the 4 things that a torque monitoring system also do?

A

Automatically operate the propeller feathering system
Assist in the automatic operation of a water injection system
Limit engine power output
Balance power output between engines

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26
Q

What are the 3 ways that torque is displayed in the flight deck?

A

Torque oil pressure (PSI)
Torque percentage
Direct horse-power read-out

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27
Q

What instrument indicates torque and where does it receive input from?

A

Torque meter which receives input from the torque sensing unit on the engine

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28
Q

What are 3 of the most common types of sensing units?

A

Hydro-mechanical - Converts engine oil pressure to torque signal
Electronic - Converts the twist of the power output shaft into a torque signal
Phase displacement - Consists of 2 shafts to measure torque

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29
Q

When is an engine removed?

A

For the change of time-limited parts or for the repair of damage

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30
Q

What allows engineers to catch defects before they develop?

A

Monitoring the operating parameters so a change in efficiency can be detected

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31
Q

What does analysing the operation parameters with engine trend monitoring show?

A

Deterioration of the engines efficiency or any developing defect

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32
Q

What is required for engine monitoring?

A

Data recording equipment onboard and ground-based data processing equipment are required

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33
Q

What carries out the data recording?

A

The Aircraft Condition Monitoring System (ACMS)

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34
Q

What do hydro-mechanical fuel controls need?

A

AN addiction computer for the parameter measurement, calledPower Plant Data Multiplexer (PMUX)

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35
Q

What does there Data Management Unit (DMU) do?

A

Records the data and complies rhetorical ACMS reports

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36
Q

What are 3 types of ACMS reports?

A

Routine reports
On request reports
Advisory reports

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37
Q

What does the wear of components during engine operation lead to?

A

Changes of the thermodynamic variable states within the gas path

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38
Q

How do they identify which engine module is responsible for thermodynamic change?

A

The module quality parameters
The share of each module in EGT and fuel flow changes

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39
Q

Why are the signals received from the vibration sensors filtered?

A

To identify vibration caused by the rotor system
Location of the unbalance on the fan rotor can also be found

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40
Q

What is generated during the first 4 take-offs?

A

ACMS reports?

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41
Q

What do ACMS reports contain?

A

Data for the calculation of the basic take-off performance of the engine

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42
Q

How often is a take-off report generated?

A

Every 35 take-offs

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43
Q

What condition must the aircraft be in for the generation of a cruise report?

A

A stable cruse condition

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44
Q

Where are the results of reports stored?

A

In the engine database, if results are critical a warning for the maintenance engineers is triggered

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45
Q

What us a moving contact between metallic surfaces always accompanied by?

A

Friction

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46
Q

What is friction reduced by, but what still happens?

A

An oil film, but microscopic particles of metal do wear and stay in suspension in the oil

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47
Q

What does oil give about the engine?

A

Information about its condition

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48
Q

What is complicated about the size of some metal particles?

A

They cannot be seen or felt, so they can flow around the system and through the filters, leading to damage of secondary components or failure of the system

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49
Q

How do we detect these small particles?

A

The use of a spectrometer in a process known as Spectrometric Oil Analysis Program (SOAP)

50
Q

How can metal particles be identified?

A

Visual inspections through to electron scanning microscopes, one of earliest ways being the use of chemicals

51
Q

What must be done first in an inspection?

A

Ferrous metals must be separated from non-ferrous by use of a magnet

52
Q

What type of metals can magnets pick up?

A

Cast iron
Carbon steel
Certain alloy steels
Some stainless steel

53
Q

What must you do to identify ferrous particles?

A

Use a heat-resistant beaker to boil particles in nitric acid solution?

54
Q

What colours do each ferrous metal turn after being boiled in nitric acid solution?

A

Cast iron - dark brown
Carbon steel - yellow or light brown
Stainless steel - remains unaffected

55
Q

Can non-ferrous particles be boiled in nitric acid?

A

Yes

56
Q

What colour do the non- ferrous metals turn when boiled in nitric acid?

A

Bronze - white powder
White metal - black and cause acid to turn pale green

57
Q

What does a visual inspection of Magnetic Chip Detectors (MCD) and filter elements provide?

A

An indication of the internal condition of the engine and gearbox

58
Q

When is an MCD inspection carried out?

A

Routinely or non routinely when there is a heavy landing, bird strike, or used as an acid to troubleshooting

59
Q

What are the 4 primary groups for magnetic particles?

A

Swarf
Magnetic fines
Metal flakes
Chip

60
Q

What is Swarf?

A

Unwanted material cause when engine components are machined, can be left in engine/gearbox after it is assembled

61
Q

What is the appearance of magnetic fines?

A

A black sludge, when removed looks the same as metal flakes

62
Q

Where do magnetic fines come from, are they acceptable?

A

Worn areas in the engine/gearbox, and they are normally acceptable

63
Q

What are the 4 places metal flakes can come from and how to they find out which one?

A

Ball bearings
Roller bearings
Bearing tracks
Gear teeth
Different shapes which can indicate their source

64
Q

What do gear teeth flakes looks like?

A

Shiny with an irregular shape, can look same as solder splashes

65
Q

What do chips and gear teeth fragments look like?

A

Very thick flakes or pieces of metal that usually have one smooth machined surface

66
Q

What is a boroscope inspection?

A

A visual inspection of the engine using either a rigid borescope, flexible fibrescope or an electronic imaging video probe

67
Q

What about gas turbine engines makes it so impending failure may go unnoticed?

A

They have extremely low vibration levels

68
Q

Due to the low vibration levels what is fitted, what does this do?

A

Vibration monitoring equipment fitted which will continuously monitor the vibration level of the engine

69
Q

What do modern engines use to detect engine vibrations?

A

Piezoelectric accelerometers

70
Q

What are the accelerations measured in and indicated as?

A

Inches per second (ips)
Millimeters per second (mm/s)
Indicated as a broadband reading on the flight deck

71
Q

What is the turbine engine is divided into for maintenance purposes?

A

Cold
Hot

72
Q

What is the main cause for damage to the blades in the compressor (cold) section?

A

FOD

73
Q

What is the accumulation of dirt caused by?

A

Centrifugal forces throwing the dirt outwards so they from a coat on the casing, vanes, and the compressor blades

74
Q

What does an accumulation of dirt on the compressor blades cause?

A

Reduces the aerodynamic efficiency of the blades which results in a deterioration in engine performance

75
Q

When can damage to the engine compressor blades be repaired?

A

When it doesn’t exceed the allowable limits recommended by the engine manufacturer

76
Q

What must rework of any damage be carried out by?

A

Hand, not using power tools

77
Q

What must happen prior to starting the engine?

A

An inspection of engine inlet ducts to ensure that no FOD items are there after the completion of any maintenance work

78
Q

Why is blending on the concave or convex surfaces, including the leading edge limited?

A

Due to the thin-sheet construction of hollow vanes

79
Q

When are small, shallow dents acceptable?

A

If the damage is of a rounded or gradual contour type?

80
Q

When are small, shallow dents unacceptable?

A

If it is a sharp or V-type dent, and if not cracking or tearing of vane material is evident

81
Q

When can trailing edge damage blended?

A

If one-third of the weld seam remains after repair

82
Q

When is it allowable that concave surfaces of rubber-filled vanes have cracks extending inwards?

A

If there is no suggestion of pieces breaking away

83
Q

What is one of the main factors in prolonging the service life of a turbine engine?

A

The inspection and cleaning of the hot section

84
Q

What should the entire external combustion case be inspected for before being opened?

A

Evidence of hotspots, exhaust leaks, and distortion

85
Q

What should the combustion chamber be inspected for once it has been opened?

A

Any localised overheating, cracks, or excessive wear

86
Q

What is the first-stage turbine blades and NGV inspected for?

A

Cracks, warping, FOD

87
Q

What are the combustion chamber outlet ducts and turbine nozzles inspected for?

A

Cracks, or FOD

88
Q

What is the most common defect found in the hot section?

A

Cracking

89
Q

What should you do to find out if cracks are within acceptable limits?

A

Refer to the applicable engine manufacturers service and overhaul manuals

90
Q

When should a turbine rinse be carried out?

A

In areas of high salt water or other chemicals

91
Q

What can be used to degrease engine parts?

A

Emulsion-type cleaners or chlorinated solvents

92
Q

What may be used to mark out areas that are directly exposed to the engines gas path?

A

Lightly applied layout dye or chalk

93
Q

Where can a wax marking pencil be used?

A

Parts not directly exposed to the gas path

94
Q

Where can a wax marking pencil not be used?

A

On the liner surface or a turbine rotor

95
Q

Why is the use of carbon alloy or metallic pencils not recommended?

A

Due to the possibility of causing intergranular corrosion

96
Q

What do you use to inspection the combustion chambers and covers for cracks?

A

A visible dye or fluorescent penetrant inspection method

97
Q

What is desirable during a fuel nozzle cleaning operation?

A

Filtered air passing through to carry away deposits

98
Q

Why are turbine blades more susceptible to damage?

A

Due to the extreme heat which they operate under

99
Q

What else needs to be replaced if one blades is being replaced?

A

The diametrically opposite blade

100
Q

What determines the location for the turbine blades for turbine wheels on modern engines?

A

Computer programs

101
Q

When are slight nicks and dents permissible in a turbine nozzle inlet guide vane?

A

If the depth of damage is within limits

102
Q

What provides the procedures and tolerances for checking the turbine?

A

The manufacturers overhaul manual

103
Q

What defect is the exhaust susceptible to?

A

Heat cracking

104
Q

What should you inspect the exhaust cone and nozzle for?

A

Cracks, warping, buckling, or hotspots

105
Q

Where is overhaul of the turbine engine accessories usually carried out?

A

Within an engine overhaul shop

106
Q

What does the accumulation of contaminants do?

A

Reduce the efficiency of the engine, and it can seriously affect its performance

107
Q

What builds up in the turbine and what does this do?

A

Sulphur deposits, which destroy the aerodynamic shape of the turbine blades and the nozzle guide vanes

108
Q

What will happen to the turbine blades over time if they are not cleaned?

A

Sulphur will erode their surface finish (hot corrosion)

109
Q

What is done to clean an engine, what does this avoid?

A

A scheduled rinsing of the compressor with fresh water, to avoid the harsher chemical treatment

110
Q

When can rinsing be carried out?

A

Either while motoring on the starter, or while in idle

111
Q

What is the rinsing procedure known as?

A

A desalination wash

112
Q

What is used as an anti-freeze while rinsing?

A

Isopropyl, as methanol is severely damaging to titanium

113
Q

What must happen to the ramp and run-up areas?

A

They must be swept regularly to ensure they are clear of FOD

114
Q

What are the 2 different types of FOD?

A

Internal
External

115
Q

What will airport operations regularly do?

A

Inspect and clear the runways of FOD

116
Q

What test must all engines pass?

A

A stringent test

117
Q

What does a stringent test involve?

A

Firing a frozen chicken into a running jet engine simulating flying through a severe rainstorm

118
Q

What must happen for the engine to pass the stringent test?

A

It doesn’t need to stay operation, but it must not cause damage to the rest of the aircraft

119
Q

What must the fan case be strong enough to do?

A

Contain a blade if it breaks off, and prevent damage or loss of the aircraft

120
Q

What prevents gravel from entering the open wheel wells on a gravel kitted aircraft?

A

Gravel deflectors and screens

121
Q

What reduces the airflow into the engine from the gound in a gravel kitted aircraft and why?

A

Vortex dissipation devices, to reduce the likelihood of sucking up gravel

Module 15 (18 decks)

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