T56 Fuel Systems Flashcards
Engine operating limits (ground) rpms (%) Start TIT Low rpm Normal rpm Flt Idle Take off Reverse
71.3-73.8
96.3-99.1
94.5-98.4
99-101
96.3-104.9
Maximum HP
Maximum TIT
4600SHP
1077
850, stop start
830, continue cautiously but investigate
Requirements of the engine fuel system
1) Provide the correct fuel flow for starting under all ambient conditions
2) Adjust fuel flow in response to power lever changes
3) Limit the maximum TIT obtainable
4) Regulate the fuel flow in the RPM range that the compressor is likely to stall or surge
5) Automatically maintain a selected power (TIT) regardless of aircraft speed, altitude, air temperature and BTU contents of the fuel
6) Control fuel flow in the event of propeller governor failure
7) Co ordinate fuel flow with blade angle changes in the beta (ground) range
8) Provide hydro mechanical operation
Purpose of the fuel-heather strainer
1) Heat the fuel
This is to prevent any minute water particles changing to ice and blocking the engine fuel filters
2) Strain the fuel
The FHS is the first engine fuel filter downstream of the AC fuel tanks booster pumps
What temperature does the vernatherm valve regulate fuel temperature at
4.5-21 *C
Occasions for servicing the FHS
1) During scheduled maintenance
2) After the first engine run following fuel tank maintenance
3) After 10 flying hours following fuel tank maintenance
What do you do before removing the FHS filter element from the housing?
E handle of the respective engine pulled.
This ensures the wing beam fuel shut off valve is closed prior, otherwise the wing tanks will gravity feed through the filter opening.
Fuel pump cluster contains 3 pumps known as:
1) Scroll pump. This operates on the screw type and centrifugal type principles 2) Secondary pump This is a gear type pump. 3) Primary pump
Major components of the low pressure fuel filter assemblies
1) Filter bodies/bowl
2) Filter elements
3) Filter bypass valve
4) Filter bypass pressure differential switch
AC fuel tank booster pumps supply fuel to the FHS at:
1) 30psi- no flow condition
2) 18 psi at 5000lbs/hr
The 2 gear type fuel pumps operate in either of the 2 following modes:
1) Series operation
From 0-16% and above 65%rpm
2) Parallel operation
16-65%rpm
Functions of the Secondary Check Valve
1) Prevents secondary pump discharge back to secondary inlet during primary pump failure
2) Provides alternative inlet to primary pump during secondary pump failure
3) Provides additional inlet to the primary pump during series operation due to its 10% greater capacity
4) Provide the inlet to the primary pump during paralleling operation
Functions of the Primary Check Valve
1) Prevents primary pump discharge back to primary pump inlet during secondary pump failure
2) Provides outlet from secondary pump during primary pump failure
3) Provides outlet from secondary pump during paralleling
Normal operation of the Parallel lights (1 light for each engine)
1) Lights are out from 0-16% rpm. Pump in series- no flow to fuel nozzles
2) Lights are on 16-65% rpm. Indicates paralleling mode in operation. It is normal for the primary pump failure lights to actually come on at approx 20% rpm. This is when the secondary pump pressure actually reaches 15- psi
3) Lights are out above 65% rpm. Pump in series for normal engine on speed conditions
Indications of Primary pump failure
1) Parallel light on between 65-100%rpm
Other faults which illuminate the paralleling light above 65% rpm
1) SSC 65% switch failure
2) Paralleling pressure switch US
3) Paralleling valve stuck open
Indications of Secondary pump failure
1) Paralleling light out between 16-65 % rpm on next engine start
Other faults which fail to illuminate the paralleling light between 16-65% rpm
1) Paralleling pressure switch US
2) Paralleling valve stuck open
3) Bulb US
Indications of Scroll pump failure
The amber ‘Pressure Low’ light on the fuel management panel illuminates. However, the scroll pump bypass valve opens at 2 psi. The low pressure fuel filters are bypassed. Fuel is ported directly to the secondary pump inlet.
