15.21 Flashcards
When would maintenance personnel have to operate a gas turbine engine?
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
How many thrust levers are there?
1 for each engine
What has to happen before the thrust reversers can be deployed?
Throttles must be in idle
What 2 things must you do before any engine start?
Confirm there is free movement of the engine
Clear area of FOD
What must be checked before positioning the aircraft?
The aircraft technical logbook for any outstanding entries that would prevent aircraft being moved or started
What must be ensured before positioning an aircraft for an engine run?
Undercarriage is down and locked
Oil levels are satisfactory, all panels secure
Sufficient fuel for ground run
Clear of FOD
How must the aircraft be positioned when doing a ground run?
Aircraft positioned into wind
Chocks fitted
Brakes applied
Ensure clear of buildings and other aircraft up to a 10 meters in front
Why would a fire service possibly be required?
If ground running with cowling open or carrying out a pressure engine run
When engines are running, what can be done if required?
Engine trimming
What shortens an engines operational life?
The more the engine is heated up and cooled down (do not increase above idle more than absolutely necessary)
Why are both engines run together?
To prevent an asymmetry problems when engines are running (one is more powerful than the other)
What must the oldest engine be used as when carrying out an acceleration check?
To use as a datum engine (reference)
What is done before cutting fuel off an engine?
The throttle levers are moved to idle
How long should you leave the engine to cool at idle before shutting down and why?
5 minutes to prevent possible seizure of the rotors
What are the 4 types of indications for engine monitoring?
Engine Pressure Ratio (EPR)
Rotor speed, N1, N2, N3
Fuel Flow (FF)
Exhaust Gas Temperature (EGT)
How do we measure EPR?
The ratio of the jet pipe pressure to the compressor inlet pressure is measured, giving an indication of thrust output
What does the N1 indication show?
The rotor speed of the low-pressure spool
What does the N2 indication show?
The high-pressure spool limit and speed switching during the engine start
What is FF used to monitor?
Fuel consumption during flight and for trend monitoring purposes
What is EGT used to recognise and prevent?
Overheating
How do centrifugal compressor engines measure engine power?
By comparing the relationship between engine RPM and Jet Pipe Temperature (JPT)
Why can’t axial flow bypass engines use the same method as centrifugal?
As there is no direct relationship between engine RPM and thrust
How to they measure engine power in an axial flow engine?
Compare static ambient pressure and exhaust gas pressure
What do torque monitoring systems indicate?
Indicate the power developed by a turbo-prop or turbo-shaft engines
What are the 4 things that a torque monitoring system also do?
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
What are the 3 ways that torque is displayed in the flight deck?
Torque oil pressure (PSI)
Torque percentage
Direct horse-power read-out
What instrument indicates torque and where does it receive input from?
Torque meter which receives input from the torque sensing unit on the engine
What are 3 of the most common types of sensing units?
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
When is an engine removed?
For the change of time-limited parts or for the repair of damage
What allows engineers to catch defects before they develop?
Monitoring the operating parameters so a change in efficiency can be detected
What does analysing the operation parameters with engine trend monitoring show?
Deterioration of the engines efficiency or any developing defect
What is required for engine monitoring?
Data recording equipment onboard and ground-based data processing equipment are required
What carries out the data recording?
The Aircraft Condition Monitoring System (ACMS)
What do hydro-mechanical fuel controls need?
AN addiction computer for the parameter measurement, calledPower Plant Data Multiplexer (PMUX)
What does there Data Management Unit (DMU) do?
Records the data and complies rhetorical ACMS reports
What are 3 types of ACMS reports?
Routine reports
On request reports
Advisory reports
What does the wear of components during engine operation lead to?
Changes of the thermodynamic variable states within the gas path
How do they identify which engine module is responsible for thermodynamic change?
The module quality parameters
The share of each module in EGT and fuel flow changes
Why are the signals received from the vibration sensors filtered?
To identify vibration caused by the rotor system
Location of the unbalance on the fan rotor can also be found
What is generated during the first 4 take-offs?
ACMS reports?
What do ACMS reports contain?
Data for the calculation of the basic take-off performance of the engine
How often is a take-off report generated?
Every 35 take-offs
What condition must the aircraft be in for the generation of a cruise report?
A stable cruse condition
Where are the results of reports stored?
In the engine database, if results are critical a warning for the maintenance engineers is triggered
What us a moving contact between metallic surfaces always accompanied by?
Friction
What is friction reduced by, but what still happens?
An oil film, but microscopic particles of metal do wear and stay in suspension in the oil
What does oil give about the engine?
Information about its condition
What is complicated about the size of some metal particles?
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
How do we detect these small particles?
The use of a spectrometer in a process known as Spectrometric Oil Analysis Program (SOAP)
How can metal particles be identified?
Visual inspections through to electron scanning microscopes, one of earliest ways being the use of chemicals
What must be done first in an inspection?
Ferrous metals must be separated from non-ferrous by use of a magnet
What type of metals can magnets pick up?
Cast iron
Carbon steel
Certain alloy steels
Some stainless steel
What must you do to identify ferrous particles?
Use a heat-resistant beaker to boil particles in nitric acid solution?
What colours do each ferrous metal turn after being boiled in nitric acid solution?
Cast iron - dark brown
Carbon steel - yellow or light brown
Stainless steel - remains unaffected
Can non-ferrous particles be boiled in nitric acid?
Yes
What colour do the non- ferrous metals turn when boiled in nitric acid?
Bronze - white powder
White metal - black and cause acid to turn pale green
What does a visual inspection of Magnetic Chip Detectors (MCD) and filter elements provide?
An indication of the internal condition of the engine and gearbox
When is an MCD inspection carried out?
Routinely or non routinely when there is a heavy landing, bird strike, or used as an acid to troubleshooting
What are the 4 primary groups for magnetic particles?
Swarf
Magnetic fines
Metal flakes
Chip
What is Swarf?
Unwanted material cause when engine components are machined, can be left in engine/gearbox after it is assembled
What is the appearance of magnetic fines?
A black sludge, when removed looks the same as metal flakes
Where do magnetic fines come from, are they acceptable?
Worn areas in the engine/gearbox, and they are normally acceptable
What are the 4 places metal flakes can come from and how to they find out which one?
Ball bearings
Roller bearings
Bearing tracks
Gear teeth
Different shapes which can indicate their source
What do gear teeth flakes looks like?
Shiny with an irregular shape, can look same as solder splashes
What do chips and gear teeth fragments look like?
Very thick flakes or pieces of metal that usually have one smooth machined surface
What is a boroscope inspection?
A visual inspection of the engine using either a rigid borescope, flexible fibrescope or an electronic imaging video probe
What about gas turbine engines makes it so impending failure may go unnoticed?
They have extremely low vibration levels
Due to the low vibration levels what is fitted, what does this do?
Vibration monitoring equipment fitted which will continuously monitor the vibration level of the engine
What do modern engines use to detect engine vibrations?
Piezoelectric accelerometers
What are the accelerations measured in and indicated as?
Inches per second (ips)
Millimeters per second (mm/s)
Indicated as a broadband reading on the flight deck
What is the turbine engine is divided into for maintenance purposes?
Cold
Hot
What is the main cause for damage to the blades in the compressor (cold) section?
FOD
What is the accumulation of dirt caused by?
Centrifugal forces throwing the dirt outwards so they from a coat on the casing, vanes, and the compressor blades
What does an accumulation of dirt on the compressor blades cause?
Reduces the aerodynamic efficiency of the blades which results in a deterioration in engine performance
When can damage to the engine compressor blades be repaired?
When it doesn’t exceed the allowable limits recommended by the engine manufacturer
What must rework of any damage be carried out by?
Hand, not using power tools
What must happen prior to starting the engine?
An inspection of engine inlet ducts to ensure that no FOD items are there after the completion of any maintenance work
Why is blending on the concave or convex surfaces, including the leading edge limited?
Due to the thin-sheet construction of hollow vanes
When are small, shallow dents acceptable?
If the damage is of a rounded or gradual contour type?
When are small, shallow dents unacceptable?
If it is a sharp or V-type dent, and if not cracking or tearing of vane material is evident
When can trailing edge damage blended?
If one-third of the weld seam remains after repair
When is it allowable that concave surfaces of rubber-filled vanes have cracks extending inwards?
If there is no suggestion of pieces breaking away
What is one of the main factors in prolonging the service life of a turbine engine?
The inspection and cleaning of the hot section
What should the entire external combustion case be inspected for before being opened?
Evidence of hotspots, exhaust leaks, and distortion
What should the combustion chamber be inspected for once it has been opened?
Any localised overheating, cracks, or excessive wear
What is the first-stage turbine blades and NGV inspected for?
Cracks, warping, FOD
What are the combustion chamber outlet ducts and turbine nozzles inspected for?
Cracks, or FOD
What is the most common defect found in the hot section?
Cracking
What should you do to find out if cracks are within acceptable limits?
Refer to the applicable engine manufacturers service and overhaul manuals
When should a turbine rinse be carried out?
In areas of high salt water or other chemicals
What can be used to degrease engine parts?
Emulsion-type cleaners or chlorinated solvents
What may be used to mark out areas that are directly exposed to the engines gas path?
Lightly applied layout dye or chalk
Where can a wax marking pencil be used?
Parts not directly exposed to the gas path
Where can a wax marking pencil not be used?
On the liner surface or a turbine rotor
Why is the use of carbon alloy or metallic pencils not recommended?
Due to the possibility of causing intergranular corrosion
What do you use to inspection the combustion chambers and covers for cracks?
A visible dye or fluorescent penetrant inspection method
What is desirable during a fuel nozzle cleaning operation?
Filtered air passing through to carry away deposits
Why are turbine blades more susceptible to damage?
Due to the extreme heat which they operate under
What else needs to be replaced if one blades is being replaced?
The diametrically opposite blade
What determines the location for the turbine blades for turbine wheels on modern engines?
Computer programs
When are slight nicks and dents permissible in a turbine nozzle inlet guide vane?
If the depth of damage is within limits
What provides the procedures and tolerances for checking the turbine?
The manufacturers overhaul manual
What defect is the exhaust susceptible to?
Heat cracking
What should you inspect the exhaust cone and nozzle for?
Cracks, warping, buckling, or hotspots
Where is overhaul of the turbine engine accessories usually carried out?
Within an engine overhaul shop
What does the accumulation of contaminants do?
Reduce the efficiency of the engine, and it can seriously affect its performance
What builds up in the turbine and what does this do?
Sulphur deposits, which destroy the aerodynamic shape of the turbine blades and the nozzle guide vanes
What will happen to the turbine blades over time if they are not cleaned?
Sulphur will erode their surface finish (hot corrosion)
What is done to clean an engine, what does this avoid?
A scheduled rinsing of the compressor with fresh water, to avoid the harsher chemical treatment
When can rinsing be carried out?
Either while motoring on the starter, or while in idle
What is the rinsing procedure known as?
A desalination wash
What is used as an anti-freeze while rinsing?
Isopropyl, as methanol is severely damaging to titanium
What must happen to the ramp and run-up areas?
They must be swept regularly to ensure they are clear of FOD
What are the 2 different types of FOD?
Internal
External
What will airport operations regularly do?
Inspect and clear the runways of FOD
What test must all engines pass?
A stringent test
What does a stringent test involve?
Firing a frozen chicken into a running jet engine simulating flying through a severe rainstorm
What must happen for the engine to pass the stringent test?
It doesn’t need to stay operation, but it must not cause damage to the rest of the aircraft
What must the fan case be strong enough to do?
Contain a blade if it breaks off, and prevent damage or loss of the aircraft
What prevents gravel from entering the open wheel wells on a gravel kitted aircraft?
Gravel deflectors and screens
What reduces the airflow into the engine from the gound in a gravel kitted aircraft and why?
Vortex dissipation devices, to reduce the likelihood of sucking up gravel
