Gas Turbne Starting Flashcards
Engine starting first step after start switch set to ON
Opens spar valves and activates starter motor turns the HP compressor
After the HP compressor has started running what happens to the the PRSOV
HP shut off valve (PRSOV) opened allowing fuel to enter the combustor
Start Sequence
Ignition On/Starter Motor On
HP fuel on/N2 compressor starts to spin
Light up occurs after HP shut off valve opened and fuel introduced
Starter motors continues until self sustaining RPM at 30%
Cut out starter motor
Stabilises at ground idle
Dry start
Fuel fails to flow no light up/no EGT rise
Stagnating LOW rpm
Hung Start
Low and stagnating RPM
Low fuel flow
High EGT
Too low pneumatic starter pressure before fuel supplied to sustain combustion - engine fails to accelerate
Engine lights but fails to accelerate
Can be a result of compressor stall or surge
Hot Start
Rapid rise in EGT must be shut down asap
Continues to accelerate
Could be exceed fuel in combustor
Causes:
Early stare cut out
Fuel mis scheduling
Strong tailwinds
Very low rpm
Wet Start
Engine fails to light up but RPM stabilise at low value while unburned fuel is sprayed into combustion chamber
Low/stable RPM
No EGT rise
Some indicated fuel flow
Run a dry run
No rotation on start
Most likely failure of engine starting system
No FADEC indications
FADEC failure = engine indications blank engines will run wont be controllable with thrust lever
Multi Spool Start
N2 compressor starts rotating first
Airborne Relighting
Altitude needs to be below 25,000ft and speed needs to be sufficient
Re light envelope
Thrust Indications are
Engine pressure ratio
Speed of the fan (N1)
Torque
Engine pressure ratio is
Jet pipe pressure to inlet pressure
EPR is useful for
Indicating thrust
What happens if P1 becomes blocked on EPR
Pressure may overread as inlet pressure will not be registering correctly
How is power determines on turbo propeller engine
Torque
Engine health parameters
Oil pressure/temp/quantity
Vibration
Fuel flow
De Rating
Rated thrust of engine reduced
Via FMS CDU
Apply a lower maximum thrust limit on engine
Increases engine life
- cannot be overridden by thrust levers
Flex thrust - assumed temperature method
Artificially inputting high ambient temp on FMS
Does allow max thrust if needed
FADEC major functions
Automatic thrust rating control
Engine operation within safe limits
Fully automatic engine starting
Thrust reverser control
Engine over speed/EGT protection function
Engine monitoring and help for maintenance and troubleshooting
FADEC power sources
Dedicated FADEC power sources from different bus bars
Flat Rated
If OAT exceeds limit thrust is limited
This ensure guaranteed value of thrust up to a certain OAT
DC trembler
Generates a higher voltage to the igniters via DC current to the transformer.
