15.21 Engine Monitoring and Ground Operation Flashcards
What must be done prior to positioning an aircraft?
The logbook must be checked incase there are outstanding entries that may prevent aircraft movement or engine start up
How far must objects be away from the front of the engine if performing a ground run?
Up to 10 metres (30 feet)
With the engine running, where are you allowed to approach the engine?
Through the access corridor (only at idle!)
What type of fire extinguisher must be present when performing an engine ground run?
CO2
If ground running (idle or pressure running) with open engine cowlings, what must also be present?
A fire tender depending on local rules
Before ground running, who must be informed?
Air Traffic Control
What is “trimming” of an engine?
A term applied at idle speed, can be completed on idle run or on the engine test bed.
What must be known to correctly trim the idle speed of an engine?
- OAT
- barometric pressure/airfield altitude (QFE)
What is idle trim?
It is the lowest idle speed permitted by the manufacturer
How is idle trim adjusted to gain a higher idle RPM?
By turning the adjuster in the anti-clockwise direction on the FCU
In what direction do most manufacturers recommend final engine trim adjustments must be made?
The increase direction
When carrying out acceleration checks on aircraft engines, what must be used as the datum?
The oldest engine - ensuring all engines accelerate at the same rate
Before shutting down the engines, what must be done?
The electrical power should be transferred back to the GPU or APU allowing the engine to idle for approximately 3 minutes prior to closing the HP fuel cock
What are the three groups engine indications can be divided into?
- performance monitoring
- system monitoring
- condition monitoring
What is the EGT indication used to determine?
It is to recognise and prevent the critical condition of overheat
How is EPR measured?
It it the ratio of the jet pipe pressure to the fan inlet pressure
What is N1?
It is the % in relation to 100% of the design speed
How is thrust indicated on a centrifugal flow compressor engine?
The comparison of the relationship between engine RPM and jet pipe temperature (JPT)
Why can’t axial flow bypass engines use engine RPM compared to Jet pipe temperature (JPT) as the indication?
There is no direct relationship with there in an axial flow engine
What indications do axial flow bypass engines use?
EPR and N1
What happens in a power assurance test?
Engines are operated at three different thrust settings: - 50% take-off thrust - 75% take-off thrust - 100% take-off thrust These are then compared on tables
How is the thrust of a turboprop and turboshaft engine calculated?
The engine torque through the gearbox
What is engine torque of a turboprop and turboshaft engine directly proportional to?
Engine horsepower
What instrument is used in a turboshaft or turboprop aircraft to show the engine torque?
A torque meter
What two types of sensing units provide torque readings?
- electronic unit (electrical signal (twist of shaft) > torque)
- hydro-mechanical (oil pressure > torque)
When is an engine only ever removed?
- a change of time limited parts
- for the repair of damages
How is the engine data recorded on a modern aircraft?
Aircraft Condition Monitoring System (ACMS)
After the data is collected by the ACMS, what happens to it?
It is transmitted to the Data Management Unit (DMU). The reports can be printed out or sent via data-link.
What ACMS reports are used by the DMU?
- routine (fixed time intervals)
- on request (requested by pilot)
- advisory (when defined parameters are exceeded)
What is the SOAP?
Spectrographic Oil Analysis Program
- used to detect particles smaller than can be seen with the naked eye
It measures the colour and intensity of particles when burned
What are MCD for?
Magnetic chip detectors
- they monitor metal wear within the engine and attract ferrous metals in the oil
What can a borescope inspection identify?
Damage such as cracks, burn marks, hotspots and missing protective coatings
What must be done after a borescope inspection has taken place?
A duplicate inspection must be carried out and all access plugs must be refitted
Why must gas turbine engines have vibration monitoring systems?
They have very low vibration levels so issues may go unnoticed
What are used to monitor modern engine vibrations?
Piezoelectric accelerometers (measured in inches per second or millimetres per second)
Where are the piezoelectric accelerometers usually located on the engine?
- one on the fan or LP casing
- one on the turbine casing
What is looked for on a basic visual walk around inspection of an engine?
- oil, fuel or air leakages
- items that are loose, broken, chafed or otherwise damaged
What do the CAA recognise as 3 primary maintenance processes?
- Hard time
- On Condition
- Condition-Monitoring
What is hard time?
A preventative process which involves removal or items for overhaul or replacement at specified intervals.
A failure of these components would affect airworthiness
What is on-condition?
A preventative process which involves inspection/tests to ensure an item can remain in service
- Scheduled Servicing (periodic checks)
- Unscheduled Servicing (due to failure or malfunction)
What is Condition Monitoring?
Not a preventative process, but gathers information on a continuous basis. This means you can implement corrective procedures
What are the three main methods of Condition Monitoring?
- Flight deck indicators
- Ground indicators
- In flight recorders (IFR)
Why are engines running on the ground, subject to FOD?
They suffer from core depression that forms at the inlet, sucking in FOD as there is no ram compression at slow speeds
Why is FOD more damaging to Titanium manufactured engines?
- Can cause “hard rubs”
- It ignites at lower temperatures than it melts
- Low heat conductivity
During a compressor FOD inspection, if possible, what must be present?
A safety man inside the cockpit
What must be placed on the inlet when entering the engine?
A protective mat - to protect the acoustic panels
What must happen if, when inspecting an engine, the damage depth of a blade exceeds half of the maximum blending depth?
It must be rejected
What is important about blending depth of an engine blade?
It must be twice the damage depth
What is the purpose of a compressor wash?
It increases the efficiency of the engine
What is “hot corrosion”?
Contamination of sulphur deposits in the core engine due to burning fuel, which erodes the surface finish and aerodynamic shape of the blades
What is a desalination wash?
The engine is motored on the starter or on idle
- it is done periodically to remove salt deposits
What is a performance recovery wash?
This is performed the same as the destination wash, however is used when the contamination has reached a stage where the desalination wash isn’t sufficient
What, has a better cleaning action than cold water?
Hot water
What is the abrasive cleaning method?
A fine grit (coke) is sprayed into the eye of the engine whilst it is rotating
Why, in low temperature conditions is methanol not used on titanium as anti-freeze?
It is severely damaging to titanium
