Hydraulics Flashcards
how many hydraulic systems are there
3:
- system A
- system B
- Standby system
what do the hydraulics systems power
- flight controls
- leading edge slats/flaps
- trailing edge flaps
- landing gear
- wheel braking
- nose wheel steering
- thrust reversers
- APs
what components does system A supply
- ailerons
- rudder
- elevator and elevator feel
- flight spoilers (2/wing)
- ground spoilers
- alternate brakes
- no 1. thrust reverser
- AP A
- normal NWS
- landing gear
- PTU
what components does system B supply
- ailerons
- rudder
- elevator and elevator feel
- flight spoilers (2/wing)
- all slats and flaps
- normal brakes
- no. 2 thrust reverser
- AP B
- alternate NWS
- landing gear transfer unit
- auto slats
- yaw damper
how many pumps does system A + B have
each has:
- 1 engine driven pump
- 1 AC electric motor driven pump
how many pumps does the standby system have
1 AC electric motor driven pump
how much extra pressure does the engine driven pump output compared to the electric pump
6 times the output
what effect will pulling the engine fire switch have on the hydraulic system
- shuts off fluid flow to the engine driven hydraulic pump
- deactivates the “LOW PRESSURE” light
does switching the engine driven hydraulic pump switch to off turn the pump off
No, it will prevent the flow of hydraulic fluid from the pump into the system. the pump continues to operate so long as the engine is operating
what indications may appear following the loss of an engine driven hydraulic pump with high demands on the electric pump
- “LOW PRESSURE” for electric pump
- flight control “LOW PRESSURE” light
- MC + “FLT CONT” + “HYD”
what is unique for the 900 and beyond aircraft when an “OVERHEAT” occurs for the electric pumps
- will automatically remove power from the electric pump
- causes “LOW PRESSURE” light
how is the hydraulic fluid that is used for lubricating and cooling the pumps cooled before entering the reservoirs
via a heat exchanger:
- SYS A = main tank no.1
- SYS B = main tank no. 2
what is the minimum fuel required in the main tanks for the operation of the electric pumps on the ground
760kg
system A hydraulic leak
if leak in engine driven pump:
- standpipe maintains 20% in reservoir
- electric pump maintains the pressure
if leak in electric pump OR components:
- reservoir empties
system B hydraulic leak
if leak in either pump OR components:
- reservoir to approximately zero and system B pressure is lost
- 1 standpipe supplies fluid to both pumps
- with fluid at top of the standpipe there is sufficient fluid to allow for PTU operation
- does not affect standby system
what is the purpose of the PTU
provide the additional volume of fluid needed to operate the:
- auto slats
- leading edge flaps and slats
at the normal rate when SYS B EDP is inoperative
when does the PTU operate automatically
- SYS B EDP pressure drops below limits
- airborne
- (852 and before) flaps less than 15 but not up
- (853 and beyond) flaps not up
what is the purpose of the landing gear transfer unit
supply volume of hydraulic fluid needed to raise the landing gear at the normal rate when SYS A EDP volume is lost
when does the SYS B EDP supply the volume of hydraulic fluid needed to operate the landing gear transfer unit
- airborne
- no 1 engine RPM drops below a limit value
- landing gear lever is UP
- either main landing gear is not up and locked
how can the standby hydraulic system be activated
- automatically
- manually
what systems does the standby hydraulic system power
- thrust reversers
- rudder
- leading edge flaps and slats (extension only)
- standby yaw damper
how is the standby hydraulic system manually activated
- either FLIGHT CONTROL switch = ‘STBY RUD’ position
- ALTERNATE FLAPS master switch = ‘ARM’ position
what does positioning the FLIGHT CONTROL switch to STBY RUD do
- activates the standby system electric pump
- shuts off related hydraulic system pressure to ailerons, rudder, elevators (shuts the flight control shutoff valve)
- opens STBY RUD shutoff valve
- deactivates the related flight control “LOW PRESSURE” lights when STBY RUD shutoff valve opens
- allows standby system to power rudder and thrust reversers
- illuminates “STBY RUD ON” + MC + “FLT CONT”
what does positioning the ALTERNATE FLAPS master switch to the ARM position do
- activates the standby hydraulic electric pump
- closes the trailing edge bypass valve
- arms the alternate flaps position switch
- allows STBY system to power LE devices and thrust reversers
how is the standby hydraulic system automatically activated
- loss of SYS A OR B; and
- flaps extended; and
- airborne or wheel speed > 60kt; and
- flight control switch A or B hydraulic system = ON
OR - main PCU force fight monitor (FFM) trips
when the automatic operation of the standby hydraulics is initiated what happens to the system
- activates the standby electric pump
- opens the STBY RUD shutoff valve
- allows STBY system to power rudder and thrust reversers
- illuminates “STBY RUD ON + MC + “FLT CONT”
what happens if a leak occurs in the standby system
- reservoir empties
- “LOW QUANTITY” light illuminates when reservoir is about 50%
- SYS B continues to operate and the QTY drops to about 70% then stabilizes
what could cause variations in HYD QTY during normal operations
- system becomes pressurized after engine start
- raising or lowering the landing gear or leading edge devices
- cold soaking during long periods of cruise
what can cause hydraulic foaming
lack of reservoir pressure
how can foaming be recognised
- pressure fluctuations and blinking of “LOW PRESSURE”
- MC + ‘HYD’ momentarily illuminate
electric pump “OVERHEAT” light
- hydraulic fluid used to cool and lubricate the pumps has overheated
- pump itself has overheated
“LOW PRESSURE” lights
- output pressure of related pump is low (when engine fire switch is pulled = inhibited)
electric hydraulic pump switch
- ON
- OFF
- ON = powers associated electric hydraulic pump
- OFF = removes power from associated electric hydraulic pump
engine hydraulic pump switch:
- ON
- OFF
- ON = de-energizes blocking valve to allow pump pressure to enter the system (should remain on to prolong solenoid life)
- OFF = energizes blocking valve to block pump output
when does the ‘RF’ symbol on the HYD QTY indicator appear
qty < 76%
- on the ground AND both engines shutdown; OR
- after landing with flaps up during taxi-in
FLT CONTROL switches (A AND B):
- ON
- OFF
- STBY RUD
ON:
- normal operating position
OFF:
- closes flight control shutoff valves which isolates the ailerons, rudder and elevator from associated HYD SYS
STBY RUD:
- activates STBY electric pump
- opens standby rudder shutoff valve and pressurizes the standby rudder power control unit
FLT CONTROL “LOW PRESSURE” lights
- low hydraulic pressure to aileron, rudder and elevator
- deactivated when associated flight control switch = STBY RUD + standby rudder shutoff valve open
STANDBY HYD “LOW QUANTITY” light
- low quantity in standby reservoir
- always armed
STANDBY HYD “LOW PRESSURE” light
- output pressure of the standby electric pump is low
- armed only when standby pump operating (by manual or automatic activation)
STANDBY HYD “STBY RUD ON” light
when the standby hydraulic system is commanded on to pressurize the standby rudder power control unit
ALTERNATE FLAPS master switch:
- OFF
- ARM
- OFF = normal operating position
- ARM:
- closes trailing edge flap bypass valve
- activates the standby electric pump
- arms the alternate flaps position switch
