15.21 Operation and Monitoring Flashcards
What are the requirements for engine handling, operation, and monitoring during maintenance activities?
Detailed understanding of engine operation and safety during ground running
Includes procedures for confirming faults, post-maintenance checks, and ensuring safe operation.
What must be checked before starting any engine?
Engine air inlet for free movement, cleanliness of run-up enclosure, and presence of Foreign Object Debris (FOD)
Ensures safe engine operation and prevents damage.
What is a hung start?
Successful ignition but the engine does not accelerate to idle RPM
Indicates potential issues with fuel flow or engine performance.
What is a hot start?
When fuel burns inside the engine or EGT limit is exceeded during start
Requires immediate abortion of the starting procedure to avoid damage.
What are the safety requirements for engine ground running?
Restricted access to the engine, communication with flight deck, and availability of fire extinguisher
Ensures personnel safety and compliance with emergency protocols.
Fill in the blank: The engine is started using an external ground _______ , the APU, or an operating engine.
Air Power Unit
What must be checked before positioning the aircraft for engine run-up?
Technical logbook, undercarriage position, oil levels, fuel levels, and area clearance
Ensures that all conditions are safe for engine operation.
What communication is necessary before starting the engine?
Establish communication with ground crew and ATC for engine start permission
Ensures safety and proper coordination during engine operations.
What is idle trim?
Adjustment of idle speed to ensure the engine idles at the lowest RPM authorized by the manufacturer
Important for engine performance testing and efficiency.
What is the recommended cool-down time before shutting down an engine?
5 minutes at idle power
Prevents seizure of rotors and ensures even cooling of engine components.
What should be done after retarding the thrust lever to idle for engine shutdown?
Use an independent fuel cut-off lever or switch
Ensures safe shutdown and prevents damage to fuel system parts.
What is the role of the APU during engine start on multi-engine aircraft?
Supplies air pressure to the pneumatic starter on each engine
Essential for initiating the engine start process.
What must be monitored during the engine start sequence?
Engine speed indicator, oil pressure, and Exhaust Gas Temperature (EGT)
Critical for detecting potential issues during startup.
True or False: The fuel cut-off lever should be shut off immediately after the engine starts.
False
It should be turned off only after the thrust lever is retarded to idle.
What is the purpose of engine trimming?
Adjusting throttle settings and maximum thrust during engine performance testing
Ensures engines operate efficiently and uniformly.
What should be done if an engine does not light off within ten seconds after introducing fuel?
Shut off the fuel switch/lever to prevent unburned fuel accumulation
Important for safety and preventing engine damage.
What is the typical pressure required for external ground air during engine start?
Approximately 40 - 55 psi
Necessary for proper engine starting conditions.
What should be done after engine shutdown to check oil levels?
Wait 30 minutes for pressure to drop and oil to return to the oil tank
Ensures accurate oil level readings.
What is the purpose of engine monitoring systems during ground runs?
To monitor engine performance and limitations with the aircraft on the ground.
What types of instruments or displays are used for engine performance indications?
Individual instruments or display screens connected to sensors on the engine.
List the key indications used for engine monitoring.
- Engine Pressure Ratio (EPR)
- Rotor speed, N1 and N2 (and N3)
- Fuel Flow (FF)
- Exhaust Gas Temperature (EGT)
What does the Engine Pressure Ratio (EPR) indicate?
The ratio of the jet pipe pressure to the compressor inlet pressure, indicating thrust output.
What does the low-pressure rotor speed N1 indicate?
The rotor speed of the low-pressure spool as a percentage of the 100% design speed.
How is N1 related to thrust in high bypass engines?
N1 is used as a thrust indication because thrust is directly related to fan speed.
What is the purpose of high-pressure rotor speed N2 monitoring?
To monitor the high-pressure spool speed limit and control idle speeds.
What is the significance of Fuel Flow (FF) indication?
To monitor fuel consumption during flight and confirm positive fuel flow during engine start.
Why is Exhaust Gas Temperature (EGT) critical?
It helps recognize and prevent overheating; exceeding the red line requires immediate inspections.
How is gas turbine engine power output indicated for different engine types?
It varies between turbo-jet and turbo-prop/turbo-shaft engines.
What method is used to measure engine power for centrifugal compressor engines?
By comparing engine RPM and Jet Pipe Temperature (JPT).
What challenge do axial flow bypass engines face in measuring power output?
There is no direct relationship between engine RPM and thrust due to ambient temperature effects.
What method was used in early engines to indicate power output?
Comparison between static ambient pressure and exhaust gas pressure.
What is the Engine Pressure Ratio (EPR) system used for?
To compare inlet plus fan outlet pressure to exhaust gas pressure and present it as a ratio.
What thrust levels are used in a power assurance test?
- 50%
- 75%
- 100%
What information do thrust tables provide?
Thrust values for different thrust levels and operational limits that must not be exceeded.
What systems are used for torque monitoring in turbo-prop or turbo-shaft engines?
Torque monitoring systems indicating power developed to the flight deck.
What are the methods used to display torque in the flight deck?
- Torque oil pressure (in psi)
- Torque percentage
- Direct horse-power read-out
What is the function of a torque meter?
To indicate torque based on input from the torque sensing unit on the engine.
List the common types of torque sensing systems.
- Hydro-mechanical
- Electronic
- Phase displacement
How does the hydro-mechanical torque sensing system work?
It converts engine oil pressure to a torque signal.
What does the phase displacement system use to measure torque?
A shaft with two phonic wheels to compare phase differences.
What happens to the bleed openings in the torque sensing system under low power conditions?
The bleed openings are at their maximum, balancing oil pressure with thrust.
What is the purpose of trend monitoring in turbine engines?
To detect abnormal deteriorations in engine efficiency and limit operating costs.
What system is used for data recording on board an aircraft for engine trend monitoring?
Aircraft Condition Monitoring System (ACMS)
What additional computer is required for engines with hydro-mechanical fuel controls?
Power Plant Data Multiplexer (PMUX)
What does FADEC stand for?
Full Authority Digital Engine Control
What type of reports does the ACMS generate?
- Routine reports
- On request reports
- Advisory reports
What analysis identifies which engine module is responsible for changes in thermodynamic variables?
Thermodynamic Analysis
What information can be derived from oil analysis in engines?
Condition of the engine and wear rate of components.
What is the process known as Spectrometric Oil Analysis Program (SOAP) used for?
To identify metal particles in oil samples.
What do Magnetic Chip Detectors (MCD) monitor?
Ferrous material in the oil.
What are the four primary groups of magnetic particles?
- Swarf
- Magnetic fines
- Metal flakes
- Chip
What is swarf?
Unwanted material caused during the machining of engine components.
What kind of damage can boroscope inspections identify?
- Cracks
- Burn marks
- Hot spots
- Missing protective coatings
How do modern engines monitor vibration levels?
Using piezoelectric accelerometers.
What happens if engine vibration exceeds a predetermined limit?
An annunciator light will illuminate.
Fill in the blank: The data from the ACMS is sent to the _______ for analysis.
ground-based computer system
What triggers the decision for an engine change?
Development of a defect or significant deterioration in engine efficiency.
What is the role of the Data Management Unit (DMU)?
To record data and compile ACMS reports.
What is the significance of monitoring metal particle sizes in oil?
To detect changes in wear rates and potential system failures.
What is the purpose of a visual inspection of Magnetic Chip Detectors (MCD)?
To indicate the internal condition of the engine and gearbox.
How can metal flakes be identified?
By examining their shape and source.
What can an increase in magnetic fines indicate?
A bearing skid has occurred.
What should be done with all material found during inspections that does not require immediate rejection?
It should be retained to provide a history of wear types.
What is the main function of vibration monitoring equipment in gas turbine engines?
To continuously monitor the vibration level of the engine.
What does the analysis of thermodynamic data allow engineers to plan?
Engine removal and overhaul.
What is the typical frequency for generating cruise reports?
Approximately every four flight hours.
True or False: The initial quantities of metal particles in newly overhauled engines should decrease with increased engine hours.
True
What is the purpose of the ACMS take-off reports?
To calculate the basic take-off performance of the engine.
What are the two main sections of a turbine engine for inspection purposes?
Cold section and hot section
Why is maintenance of the compressor section important?
Damage to the blades can cause severe engine failure
What can cause damage to compressor blades?
Foreign object matter being sucked into the turbine engine air intakes
What is the effect of accumulation of dirt on compressor blades?
Reduces aerodynamic efficiency and deteriorates engine performance
How can poor engine acceleration and high exhaust gas temperature be rectified?
Periodic inspection, cleaning, and repair of compressor components
What is the maximum extent of minor damage that can be repaired on compressor blades?
Without exceeding the allowable limits recommended by the engine manufacturer
What inspection methods are used for repaired compressor blades?
Magnetic particle or fluorescent penetrant inspection methods
What is the recommended method for reworking damage on compressor blades?
By hand using files or emery cloth
What should be inspected when examining compressor inducers?
Cracks along the leading edges
What is Foreign Object Damage (FOD)?
Damage caused by loose objects entering the engine
What are the usual causes of compressor blade damage?
Foreign objects, excessive heat levels, and corrosive agents
What type of damage is usually acceptable on compressor stator vanes?
Corrosion pitting within allowed tolerance
What should be used to blend out damage on compressor vanes?
Appropriate blending tools to minimize material removal
What should be inspected closely on guide and swirl vanes?
Cracks and dents due to impingement of foreign particles
What is the appearance of a ‘dent’ in compressor blades?
Small, smoothly rounded hollow
What is the definition of ‘gouging’ in relation to blade damage?
Material displaced from the surface; cutting or tearing effect
What should be done if cracks branch or fork on guide vanes?
Vane replacement is required
What is the significance of inspecting the hot section of a turbine engine?
Crucial for prolonging the service life of the engine
What should be inspected on the combustion case before opening?
Evidence of hotspots, exhaust leaks, and distortions
How are cleaning operations typically performed in the hot section?
Using emulsion-type cleaners or chlorinated solvents
What is the acceptable method of marking parts during assembly?
Lightly applied layout dye or chalk
What inspection method is used for combustion chambers?
Visible dye or fluorescent penetrant inspection method
What is the acceptable limit for cracks in combustion chambers?
Two cracks progressing from a free edge must not meet
What should be done if cracks in the baffle connect more than two holes?
Repair is required
What is the procedure for cleaning fuel nozzles?
Wash with cleaning fluid and remove deposits with a soft bristle brush
What is the significance of inspecting the turbine disk?
Cracks are not normally permitted and require removal and replacement
What should be used to inspect turbine blades for stress cracks?
Strong light and magnifying glass
What indicates a potential over-temperature condition in turbine blades?
Stress cracks or deformation of the leading edges
What should be done if the turbine blade outer shroud shows wear?
Measure the thickness of the shroud
What should be suspected when stress cracks or deformation are found on the leading edges of the first-stage turbine blades?
An over-temperature condition must be suspected.
What must be checked for each individual blade when inspecting turbine blades?
Stretch and the turbine disk for hardness and stretch.
What should be done before removing turbine blades for detailed inspection?
Number each blade prior to removal.
What should be inspected on the turbine blade outer shroud?
Air seal wear.
What tool should be used to measure the thickness of the shroud at the worn area?
A micrometer or another accurate measuring device.
What is the consequence if the remaining radial thickness of the shroud is less than specified?
The stretched blade must be replaced.
Is blade tip curling within a one-half-inch square area on the leading edge usually acceptable?
Yes, if the curling is not sharp.
What is the cause for removal and replacement of a turbine blade?
Any sharp bends that may result in cracking or a piece breaking out.
What should each turbine blade be inspected for?
Cracks.
What are turbine blades subject to when it comes to replacement?
Moment-weight limitations.
What may be more economical than replacing several damaged blades?
Replacing the entire turbine assembly.
How are turbine blades made during the manufacturing build-up process?
In coded pairs and laid out in order of moment-weight.
What is marked on the rear face of the fir-tree section of the blade?
Code letters indicating the moment-weight balance.
What must be done if a blade requires replacement?
The diametrically opposite blade must also be replaced.
What determines the location for turbine blades on modern engines?
Computer programs.
What is accessible for inspection after removing the required components?
The first-stage turbine blades and turbine nozzle vanes.
What should be followed for blade limits during inspection?
The engine manufacturers overhaul manual.
Are slight nicks and dents permissible on turbine blades?
Yes, if the depth of damage is within limits.
What should be inspected on the nozzle vanes?
Nicks or cracks.
What indicates a malfunctioning fuel nozzle or combustion chamber in the exhaust section?
Hotspots on the tail cone.
What must be done to obtain accurate readings when checking clearances?
Use special tools provided by each manufacturer.
What should be thoroughly inspected in the exhaust section of the turbine engine?
Exhaust cone and exhaust nozzle for cracks, warping, buckling, or hotspots.
How should turbine engine accessories be inspected and maintained?
In accordance with the engine or aircraft manufacturers maintenance manual.
What is usually carried out within an engine overhaul shop?
Overhaul of turbine engine accessories.
What is the primary effect of contaminants in the compressor and turbine sections of an engine?
Reduces the efficiency of the engine and can seriously affect its performance.
What are the main types of contaminants found in the compressor?
Salt and pollution from industrial areas.
What is sulfidation in the context of turbine contamination?
A build-up of sulphur deposits from burning fuel that destroys the aerodynamic shape of turbine blades and nozzle guide vanes.
What is the purpose of a scheduled rinsing of the compressor with fresh water?
To avoid harsher chemical treatment required due to salt ingestion.
What is a desalination wash?
A procedure to rinse the compressor with fresh water while motoring the engine over on the starter or running at idle speed.
What is a performance recovery wash?
The application of an emulsion-type surface cleaner into the engine intake when a desalination wash is not sufficient.
How does heated water affect the cleaning action during compressor washing?
Heated water has a better cleaning action than cold water.
What is the purpose of injecting abrasive grit into the engine intake?
To provide a more vigorous treatment for cleaning, especially in centrifugal compressor engines.
What materials are commonly used for abrasive grit in engine cleaning?
Broken walnut shells or broken stones from apricots.
Why might the abrasive grit cleaning method not effectively clean turbine components?
Because the grit is mostly burnt in the combustion chambers.
What is one recommended method for cleaning fan blades?
Spraying coke, a very fine filtered abrasive, into the eye of the fan while it is rotating.
What is a critical warning regarding compressor cleaning?
All cleaning must be carried out strictly in line with the engine manufacturers’ instructions.
What type of anti-freeze should be used during low-temperature conditions with water for washing?
Isopropyl alcohol.
True or False: Methanol is safe to use as an anti-freeze during compressor washing.
False
What is Foreign Object Damage (FOD)?
An ongoing issue for the safe operation of aircraft engines, particularly turbine engines that can ingest objects from the environment.
What can ingestion of foreign matter into a turbine engine cause?
Detrimental damage and degradation of engine performance, leading to a shortened engine life.
Who must be vigilant for foreign objects in hangar and ramp areas?
All maintenance personnel.
What are the two types of FOD?
- Internal FOD
- External FOD
What is an example of internal FOD?
Loose items in the flight deck that can jam or restrict the operation of control levers.
What is Tool FOD?
A hazard caused by tools left inside the aircraft after maintenance.
What procedures do aircraft maintenance organizations have to prevent Tool FOD?
Strict tool control procedures including toolbox inventories.
What must tools used during manufacturing have?
A serial number for traceability.
Give examples of FOD.
- Aircraft parts
- Rocks
- Broken pavement
- Ramp equipment
- Parts from ground vehicles
- Rubbish
- Ice
- Bird strikes
- Dust or ash
- Tools and metal shavings
What can small parts lost by an aircraft during take-off and landing cause?
Damage to aircraft tires, fuselage, windshield, or can be ingested into another engine.
What do airport operations regularly do regarding FOD?
Inspect and clear the runways of aircraft FOD.
What type of damage can jet engines suffer from FOD?
Major damage from even small objects.
What test must all manufactured engines pass?
A test involving firing a frozen chicken into a running jet engine.
What must the engine fan case be able to do during the FOD test?
Contain a detached engine fan blade and prevent damage to the aircraft.
What design feature did Boeing add to the early B737 to prevent FOD?
Gravel deflectors on the landing gear.
What devices were included in the B737 design to reduce FOD risk?
Vortex dissipation devices.
