Gas Trubine Control And Operation

Question 1

Engine start sequence

Answer 1

~ignition commences
~air start velve opens
~min fuel is delivered into the primary zone (HPSOV)

Question 2

Types of the starter motor

Answer 2

~air pneumatic starter :driven by compressor air and controller by an air start valve

~electrical strter/genrator : use don More electric a/c
~during strat ac electric spins motor truning the accesory gearbox
~once at ground idle,the sys flips to genrator mode

Question 3

Start malfunctions

Answer 3

It may be that 15 min its needed between each cycle of starting an engine to allow the starter motor to cool down

Abnorml,
~dry start
~hung start >>( 
~hot start
~wet start

In addition may result in a tailpipe fire
~this will not illluminate an eng warning
~it may or may not be indicate through a high EGT
~the eng should be shut down ,any fire extinguisher and eng should be examined for damaged

Question 4

Dry strat

Answer 4

~low rpm
~no egt rise
~no fuel flwo
~maybe malfunction of the HPSOV

Question 5

Hung start

Answer 5

Low and stagnating rpm
High egt
Low fuel flow

~low bleed pressure
~engine failing to reach self sustaining speed

Question 6

Hot strat

Answer 6

~normal increase in rpm
~rapid excessive egt rise
~normal fuel flow

~possible following a previous failled strat attempt

Question 7

Wet start

Answer 7

~low and stagnating rpm
~no egt rise
~some indicated feul flow

A dry run (clow trhough) should be carried out

Question 8

Mutpi spool eng start

Answer 8

~at ground idle ther will be a marked difference in rotational speeds between N1 and N2
~n1 20/25%
~n2 50/60%

~flight idle only availble in fllight is a higher idle setting allowing the eng to respond to any speed increase quicker

Question 9

Airborne relight

Answer 9

Starting mean sin the ground
Relighting means strating in the air

~starter motor circuit will not be required as the eng will be windmilling
~altitude and airspeed must be considered into account
Usually below 25000ft and 250kts

Question 10

Thrust indications

Answer 10

~max take off : this is the max allowed ,usually time limited
~max continuous :the maximum thrust that can be used continuosly
~go around: might have have different N1 or EPR values
~max climb: used for routine all engines climb

Question 11

Epr and thrust indications

Answer 11

~engine pressure ratio
~accurate method to indicate pressure thrust
~copares the pressure in the intake
~if sensors beomecs unavailble the eng revert to N1 trhust settings

Question 12

N1 and thrust indications

Answer 12

~n1 thust setting
~thrust set by a percentageof fan rpm
~Fadec will rotate N2 to a desired value in order to provide an N1 rotation and given thrust setting

Question 13

Turbo pro p torque indications

Answer 13

~percentage of maximum ,torque
~usually measured using oil pressure or an elctric wheatstone bridge
~in take off or high power conditions percentage may exceed 100% fro a limited time

Question 14

De rate and flex thrust

Answer 14

~in order to maximise engine life
~the eng will provide thrust in a worst case scenario,high altitude and high take off mass
~under all other conditions,especially cold and sea level enviroments the engine will perform better than required
~under these conditions the crew can legally plan a reuduced power take off
~two methis possibile
De rate
Felxible(flex) thrust

Question 15

De rating

Answer 15

~de rating reduces the thrust available from the max value

~for instance
If the produces a maximum of 264000lb of thrust
Its possibile to set 24000 via the fmc

~this has the effect of imposing a lower thrust limit on the engine
The Vmcg and Vmca speeds will change and are available through the performance manual

~the disadvantage of this system is full thrust is not available should it be required

Question 16

Flex tresut

Answer 16

~is another alternative mens to reducing eng trhust on take off
~the most common method is to use an assumesd temperature method
~benefit of this method id that if full thrust required the thrust levers can be set to TO/GA to disregard the flex configuration.as full thrust is available ,Vmcg and Vmca msut be calculated based on full thrust settings

Question 17

Thrust in flight ,low by pass

Answer 17

~as altitude increase outside air become less dense ,this cause a change in availble thrust
~as the mass flow of air decreases ,fadec or barometric controller will adjust the fuel flow accordingly
~ a fall in temperature will cause an increase in density ,mass flow will increase and thrust available will increase
~in the clim,the combines effects will cause

Question 18

High by pass

Answer 18

In a high pass things are broadly the same
~however ,the reduction in thrust as speed increase can be more pronounced
~this is due to lower ram effect in the by pass duct
~ram effect ,increasing mass flow as tas increase,raises the static pressure within the intake to improve compression ratio
~ as fuel consumption isproportional to temperrure ,in the cruise the high by p[ass trubofan becomes more fuel efficent
Thrust can be reduced
Fuel will be reduced

Question 19

Engine vibration indication

Answer 19

~piezo electric crystal is used to detect vibration

Question 20

Engine seizure

Answer 20

Engines one or both spools stop rotating
Lack lubrification
~failure of the compressure