15.21 Engine Monitoring and Ground Operation

Question 1

What must be done prior to positioning an aircraft?

Answer 1

The logbook must be checked incase there are outstanding entries that may prevent aircraft movement or engine start up

Question 2

How far must objects be away from the front of the engine if performing a ground run?

Answer 2

Up to 10 metres (30 feet)

Question 3

With the engine running, where are you allowed to approach the engine?

Answer 3

Through the access corridor (only at idle!)

Question 4

What type of fire extinguisher must be present when performing an engine ground run?

Answer 4

CO2

Question 5

If ground running (idle or pressure running) with open engine cowlings, what must also be present?

Answer 5

A fire tender depending on local rules

Question 6

Before ground running, who must be informed?

Answer 6

Air Traffic Control

Question 7

What is “trimming” of an engine?

Answer 7

A term applied at idle speed, can be completed on idle run or on the engine test bed.

Question 8

What must be known to correctly trim the idle speed of an engine?

Answer 8

• OAT

- barometric pressure/airfield altitude (QFE)

Question 9

What is idle trim?

Answer 9

It is the lowest idle speed permitted by the manufacturer

Question 10

How is idle trim adjusted to gain a higher idle RPM?

Answer 10

By turning the adjuster in the anti-clockwise direction on the FCU

Question 11

In what direction do most manufacturers recommend final engine trim adjustments must be made?

Answer 11

The increase direction

Question 12

When carrying out acceleration checks on aircraft engines, what must be used as the datum?

Answer 12

The oldest engine - ensuring all engines accelerate at the same rate

Question 13

Before shutting down the engines, what must be done?

Answer 13

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

Question 14

What are the three groups engine indications can be divided into?

Answer 14

• performance monitoring
• system monitoring
• condition monitoring

Question 15

What is the EGT indication used to determine?

Answer 15

It is to recognise and prevent the critical condition of overheat

Question 16

How is EPR measured?

Answer 16

It it the ratio of the jet pipe pressure to the fan inlet pressure

Question 17

What is N1?

Answer 17

It is the % in relation to 100% of the design speed

Question 18

How is thrust indicated on a centrifugal flow compressor engine?

Answer 18

The comparison of the relationship between engine RPM and jet pipe temperature (JPT)

Question 19

Why can’t axial flow bypass engines use engine RPM compared to Jet pipe temperature (JPT) as the indication?

Answer 19

There is no direct relationship with there in an axial flow engine

Question 20

What indications do axial flow bypass engines use?

Answer 20

EPR and N1

Question 21

What happens in a power assurance test?

Answer 21

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

Question 22

How is the thrust of a turboprop and turboshaft engine calculated?

Answer 22

The engine torque through the gearbox

Question 23

What is engine torque of a turboprop and turboshaft engine directly proportional to?

Answer 23

Engine horsepower

Question 24

What instrument is used in a turboshaft or turboprop aircraft to show the engine torque?

Answer 24

A torque meter

Question 25

What two types of sensing units provide torque readings?

Answer 25

- electronic unit (electrical signal (twist of shaft) > torque) - hydro-mechanical (oil pressure > torque)

Question 26

When is an engine only ever removed?

Answer 26

- a change of time limited parts | - for the repair of damages

Question 27

How is the engine data recorded on a modern aircraft?

Answer 27

Aircraft Condition Monitoring System (ACMS)

Question 28

After the data is collected by the ACMS, what happens to it?

Answer 28

It is transmitted to the Data Management Unit (DMU). The reports can be printed out or sent via data-link.

Question 29

What ACMS reports are used by the DMU?

Answer 29

- routine (fixed time intervals) - on request (requested by pilot) - advisory (when defined parameters are exceeded)

Question 30

What is the SOAP?

Answer 30

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

Question 31

What are MCD for?

Answer 31

Magnetic chip detectors | - they monitor metal wear within the engine and attract ferrous metals in the oil

Question 32

What can a borescope inspection identify?

Answer 32

Damage such as cracks, burn marks, hotspots and missing protective coatings

Question 33

What must be done after a borescope inspection has taken place?

Answer 33

A duplicate inspection must be carried out and all access plugs must be refitted

Question 34

Why must gas turbine engines have vibration monitoring systems?

Answer 34

They have very low vibration levels so issues may go unnoticed

Question 35

What are used to monitor modern engine vibrations?

Answer 35

Piezoelectric accelerometers (measured in inches per second or millimetres per second)

Question 36

Where are the piezoelectric accelerometers usually located on the engine?

Answer 36

- one on the fan or LP casing | - one on the turbine casing

Question 37

What is looked for on a basic visual walk around inspection of an engine?

Answer 37

- oil, fuel or air leakages | - items that are loose, broken, chafed or otherwise damaged

Question 38

What do the CAA recognise as 3 primary maintenance processes?

Answer 38

- Hard time - On Condition - Condition-Monitoring

Question 39

What is hard time?

Answer 39

A preventative process which involves removal or items for overhaul or replacement at specified intervals. A failure of these components would affect airworthiness

Question 40

What is on-condition?

Answer 40

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)

Question 41

What is Condition Monitoring?

Answer 41

Not a preventative process, but gathers information on a continuous basis. This means you can implement corrective procedures

Question 42

What are the three main methods of Condition Monitoring?

Answer 42

- Flight deck indicators - Ground indicators - In flight recorders (IFR)

Question 43

Why are engines running on the ground, subject to FOD?

Answer 43

They suffer from core depression that forms at the inlet, sucking in FOD as there is no ram compression at slow speeds

Question 44

Why is FOD more damaging to Titanium manufactured engines?

Answer 44

- Can cause “hard rubs” - It ignites at lower temperatures than it melts - Low heat conductivity

Question 45

During a compressor FOD inspection, if possible, what must be present?

Answer 45

A safety man inside the cockpit

Question 46

What must be placed on the inlet when entering the engine?

Answer 46

A protective mat - to protect the acoustic panels

Question 47

What must happen if, when inspecting an engine, the damage depth of a blade exceeds half of the maximum blending depth?

Answer 47

It must be rejected

Question 48

What is important about blending depth of an engine blade?

Answer 48

It must be twice the damage depth

Question 49

What is the purpose of a compressor wash?

Answer 49

It increases the efficiency of the engine

Question 50

What is “hot corrosion”?

Answer 50

Contamination of sulphur deposits in the core engine due to burning fuel, which erodes the surface finish and aerodynamic shape of the blades

Question 51

What is a desalination wash?

Answer 51

The engine is motored on the starter or on idle | - it is done periodically to remove salt deposits

Question 52

What is a performance recovery wash?

Answer 52

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

Question 53

What, has a better cleaning action than cold water?

Answer 53

Hot water

Question 54

What is the abrasive cleaning method?

Answer 54

A fine grit (coke) is sprayed into the eye of the engine whilst it is rotating

Question 55

Why, in low temperature conditions is methanol not used on titanium as anti-freeze?

Answer 55

It is severely damaging to titanium