HYDRAULIC SYSTEMS

If there is any conflicting information, your FCOM shall be the overriding reference.



Q1. How is Yellow Hyd. Sys pressurized?
A1. The Yellow hydraulic system is pressurized by a pump driven by engine 2. An electric pump can also pressurize the yellow system, which allows yellow
hydraulics to be used on the ground when the engines are stopped. Crew members can also use a hand pump to pressurize the yellow system in order to operate the cargo doors when no electrical power is available.
Q2. In which of the hydraulic systems, engine driven pumps are installed?
A2. Green and Yellow.​
Q3. Name some of the major users of the GREEN system?
A3. Some of the major users of Green system :-
–> Landing Gear
–> Slats/Flaps
–> Normal Brakes
–> Rev Eng 1
–> Yaw Damper 1
–> Stabilizer
–> Some Flt. Control surfaces
Q4. Name some of the major users of the BLUE system?
A4. Some of the major users of Blue system :-
–> Emerg. Gen.
–> Slats
–> Rudder
–> Some Flt. control surfaces
Q5. Name some of the major users of the YELLOW system?
A5. Some of the major users of Yellow system :-
–> Flaps
–> Alt./Parking brake
–> Rev Eng 2
–> Yaw Damper 2
–> Rudder
–> Stabilizer
–> Nose Wheel Steering
Q6. Name the components in Green Hyd. system?
A6. Components in Green Hydraulic system :-
–> Eng 2 Pump
–> PTU
–> Green Reservoir
–> Eng 1 FSOV
–> Accumulator
–> Priority Valve

Q7. When does Blue Pump energize,{with the a/c on the ground and the blue electric pump switch in AUTO}?
A7. The Blue pump energizes on the ground with the Blue Elec. pump s/w in AUTO when either engine is running or if the crew has pressed the BLUE PUMP OVRD P/b on the Maintenance panel.
Q8. What is the purpose of the priority valve installed in Hydraulic Systems?
A8. The priority valves cut off hydraulic power to heavy load users if hydraulic pressure in a system gets low. In the event of low hydraulic pressure, the priority valves maintain the operation
of essential systems by cutting off hydraulic power to heavy load users.
Q9. What happens to the yellow hydraulic system when a cargo door is being opened or closed?
A9. When a crewman sets the lever of the cargo door manual selector valve to open or close, it inhibits the operation of other yellow system function (Except Alternate braking & Eng 2 Reverser). The 'OFF' Light comes on in the Yellow Elec. pump P/b s/w.
Q10. What is the purpose of the engine fire shutoff valves?
A10. Each of the Green and Yellow systems has a FSOV in its line upstream of its EDP. The flight crew can close it by pushing the ENG 1(2) FIRE P/b . The FSOV isolates the hydraulic system from its respective engine to prevent the spread of fire.
Q11. What is the PTU and what is its purpose?
A11. PTU is short for Power Transfer Unit. It is s bi-directional power transfer unit which enables the Yellow system to pressurize the Green system & vice versa.
It comes into action automatically when the differential pressure between the Green and the Yellow systems is greater than 500 psi.
Q12. Is it possible to pressurize the green hydraulic system on the ground via the PTU?
A12. Yes.
Q13. During cockpit preparation if you start yellow electric pump, will green hyd. Sys. get pressurized via PTU?
A13. Yes.
Q14. When does the PTU operate?
A14. The PTU operates when the differential pressure between the Green and Yellow systems is more than 500 psi.
Q15. Will the PTU operate during Cargo Door operation?
A15. No.
Q16. What are the conditions when PTU will not run {inhibited}, even if there is a differential pressure between Green & Yellow is more than 500 psi?
A16. The following are the conditions when the PTU is inhibited from operating :-
–> PTU inhibited during first engine start
–> If Green/Yellow Reservoir overheats
–> If Green/Yellow reservoir has low air pressure
–> If Green/yellow reservoir has low fluid level
–> Parking Brake ON and only one ENG MAST ON
–> NWS in towing position and Parking brake ON
Q17. When is the PTU self tested?
A17. PTU is self tested during the second engine start.
Q18. During PTU Operation, can fluid be transferred between green & yellow hydraulic systems?
A18. No.
Q19. PTU transfers only pressure. It does not transfer liquid. Is it true or false?
A19. True.
Q20. If there is a Lo Level in one of the Hyd. System, Is this hydraulic system still available or lost for the remainder of the flight?
A20. Lost.
Q21. If there is a Lo Level or OVERHEAT of the reservoir in G or Y Hyd. Sys, is PTU available?
A21. No.
Q22. Which of the Hyd. Sys is pressurized by RAT?
A22. Blue.
Q23. How can the RAT be deployed manually?
A23. The flight crew may extend the RAT at any time by pressing the RAT MAN ON P/b on the HYD panel on the overhead or by pressing the MAN ON P/b on EMER ELEC PWR panel o the overhead.
Q24. Why there are two guarded p/bs for extending RAT manually on overhead panels?
A24. The 2 guarded P/b's are on two different panels on the Overhead. One on the HYD panel and the other on EMER ELEC PWR panel. By pressing the RAT MAN ON P/b on HYD panel, the RAT powers only the hydraulic system through the Blue system. By pressing the MAN ON P/b on EMER ELEC PWR panel, the RAT also powers the EMER GEN for emergency electrical power generation.
Q25. If there is a Low Level in Blue Hyd. System, can RAT power Blue Hyd. system if required?
A25. No.
Q26. When do you get FAULT light in G or Y ENG PUMP s/w p/b?
A26. The FAULT Light comes on and ECAM caution appears if :-
(a) The reservoir level is low
(b) The reservoir overheats
(c) The reservoir air pressure is low
(d) The pump pressure is low (inhibited on ground when the engine is stopped).
Q27. When do you get FAULT light in PTU s/w p/b?
A27. The FAULT Light comes on Amber and cautions appears on ECAM if :-
(a) The Green or the Yellow reservoir overheats.
(b) The Green or the Yellow reservoir has low air pressure.
(c) The Green or the Yellow reservoir has a low fluid level.
Q28. If you have AIR DUAL BLEED FAULT, will there be loss of Hyd. reservoir pressurization? Give reason supporting your answer?
A28. Yes, there will be loss of Hyd. reservoir pressurization. This is because the system automatically takes bleed air pressure from the cross-bleed duct, but in case of dual bleed fault, there is no bleed pressure from both engines, hence even with the cross-bleed valve open, there would be no air pressure to pressurize the reservoirs.
Q29. When do you get FAULT light in BLUE Elect pump? Will there be FAULT light in PTU also at that time? Why?
A29. FAULT Light come son Amber if :-
–> The reservoir level is low
–> The reservoir overheats
–> The air pressure in the reservoir is low
–> The pump is delivering low pressure
–> The pump overheats.
No, there won't be a Fault Light in PTU at that time as the PTU is not connected to the Blue system.
Q30. When do you get FAULT light in YELLOW Elect pump? Will there be FAULT light in PTU also at that time? Why?
A30. The FAULT Light in Yellow Elec. pump comes on when :-
–> The reservoir level is low
–> The reservoir overheats
–> The air pressure in the reservoir is low
–> The pump is delivering low pressure
–> The pump overheats.
The FAULT light in the PTU will be on at the same time in case of the FAULT light in Yellow Elec. pimp coming due to Reservoir level being low/Air pressure in reservoir being low or overheat in the reservoir. This is because in these cases the PTU is inhibited from operation.
Q31. What happens when you press the guarded RAT MAN ON p/b on Hyd. panel?A31. The RAT extends and powers the Blue system.
Q32. How to reset HYD PTU FAULT if it appears during engine start? Why it will come during engine start?
A32. It can be reset by switching the Yellow Elec. pump ON, then OFF. It comes on when the second engine is started within 40 seconds of cargo door operation. As the PTU is inhibited from operation during cargo door operation and it is tested during the second engine start, the Fault comes on indicating that the PTU is not operating.
Q33. Why do you switch off PTU first in HYD OVHT or HYD LO LVL in G or Y Hyd. System before switching ENG PUMP OFF?A33. This is done so as to prevent the PTU from automatically coming on and running the respective faulty hydraulic system which has an Overheat condition or a low fluid level, thereby overheating the PTU itself and ultimately leading to the good hydraulic system also getting into an overheat condition.
Q34. If you have lost green hydraulics system, what other check list may have to be followed by the crew in approach?A34. "L/G GRVTY EXTENSION" procedure would also have to be followed.
Q35. If you lose yellow hydraulic system in flight, which of the systems are not available? During landing roll or after landing when you come for parking what caution has to be followed with Y SYS lost?
A35. The following systems are lost :-
–> Yellow Hyd
–> SPLR 2+4
–> CAT 3 DUAL
–> ALTN. BRAKE
–> REVERSER 2
–> CARGO DOOR
–> YAW DAMPER 2
After landing, for parking, the Parking Brake may be inoperative, hence parking brake should not be used and chocks should be in place before shutting down Engine 1.
Q36. If there is a Lo Level in Yellow Hyd. System in flight, will you get NWS after landing?
A36. Yes.
Q37. What is the purpose of the hand pump?
A37. The hand pump can be used to pressurize the Yellow system in order to operate the cargo doors when no electrical power is available.
From ECAM HYD page:
Q38. When will the Reservoir quantity symbol becomes Amber? Which ECAM caution will be generated?
A38. The reservoir quantity symbol becomes Amber for the following values :-
(a) <3.5 L for Green/Yellow
(b) <2.4 L for Blue.
ECAM caution :- HYD G(Y)(B) RSVR LO LVL .
Q39. When does Reservoir LO AIR PRESS appear Amber on HYD page? Which ECAM caution will be generated?
A39. Reservoir "LO AIR PRESS" appears Amber when the air pressure for the indicated reservoir drops below normal.
(a) For Green/Yellow/Blue, if reservoir air pressure <22 psi
ECAM caution generated :- HYD G(Y)(B) RSVR OVHT.
Q40. When does Reservoir OVHT appear Amber on HYD page? Which ECAM caution will be generated?
A40. The reservoir overheat appears Amber when the temp. of the returning hydraulic fluid temp. at the inlet to its reservoir is above normal, i.e, if fluid temp.> 93 degrees Celsius.
ECAM caution generated :- HYD G(Y)(B) RSVR OVHT
Q41. Is there any difference in ELEC OVHT and Reservoir OVHT on HYD page? What is that?
A41. Yes. The difference is that in the former, the pump has overheated whereas in the latter, the hydraulic fluid temp. is high.
Q42. By switching PTU OFF, what change do you see on HYD page?
A42. The PTU legend on HYD page becomes Amber.
Q43. You will be seeing letter 1 and 2 near ENG PUMP on HYD page. What happens to it when N2 is below idle?
A43. It becomes Amber.



Credit : Sourav Singh

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