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B737 > Hydraulics > Flashcards

Hydraulics Flashcards

1
Q

how many hydraulic systems are there

A

3:
- system A
- system B
- Standby system

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2
Q

what do the hydraulics systems power

A
  • flight controls
  • leading edge slats/flaps
  • trailing edge flaps
  • landing gear
  • wheel braking
  • nose wheel steering
  • thrust reversers
  • APs
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3
Q

what components does system A supply

A
  • 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
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4
Q

what components does system B supply

A
  • 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
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5
Q

how many pumps does system A + B have

A

each has:
- 1 engine driven pump
- 1 AC electric motor driven pump

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6
Q

how many pumps does the standby system have

A

1 AC electric motor driven pump

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7
Q

how much extra pressure does the engine driven pump output compared to the electric pump

A

6 times the output

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8
Q

what effect will pulling the engine fire switch have on the hydraulic system

A
  • shuts off fluid flow to the engine driven hydraulic pump
  • deactivates the “LOW PRESSURE” light
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9
Q

does switching the engine driven hydraulic pump switch to off turn the pump off

A

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

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10
Q

what indications may appear following the loss of an engine driven hydraulic pump with high demands on the electric pump

A
  • “LOW PRESSURE” for electric pump
  • flight control “LOW PRESSURE” light
  • MC + “FLT CONT” + “HYD”
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11
Q

what is unique for the 900 and beyond aircraft when an “OVERHEAT” occurs for the electric pumps

A
  • will automatically remove power from the electric pump
  • causes “LOW PRESSURE” light
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12
Q

how is the hydraulic fluid that is used for lubricating and cooling the pumps cooled before entering the reservoirs

A

via a heat exchanger:
- SYS A = main tank no.1
- SYS B = main tank no. 2

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13
Q

what is the minimum fuel required in the main tanks for the operation of the electric pumps on the ground

A

760kg

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14
Q

system A hydraulic leak

A

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

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15
Q

system B hydraulic leak

A

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

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16
Q

what is the purpose of the PTU

A

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

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17
Q

when does the PTU operate automatically

A
  • SYS B EDP pressure drops below limits
  • airborne
  • (852 and before) flaps less than 15 but not up
  • (853 and beyond) flaps not up
18
Q

what is the purpose of the landing gear transfer unit

A

supply volume of hydraulic fluid needed to raise the landing gear at the normal rate when SYS A EDP volume is lost

19
Q

when does the SYS B EDP supply the volume of hydraulic fluid needed to operate the landing gear transfer unit

A
  • airborne
  • no 1 engine RPM drops below a limit value
  • landing gear lever is UP
  • either main landing gear is not up and locked
20
Q

how can the standby hydraulic system be activated

A
  • automatically
  • manually
21
Q

what systems does the standby hydraulic system power

A
  • thrust reversers
  • rudder
  • leading edge flaps and slats (extension only)
  • standby yaw damper
22
Q

how is the standby hydraulic system manually activated

A
  • either FLIGHT CONTROL switch = ‘STBY RUD’ position
  • ALTERNATE FLAPS master switch = ‘ARM’ position
23
Q

what does positioning the FLIGHT CONTROL switch to STBY RUD do

A
  • 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”
24
Q

what does positioning the ALTERNATE FLAPS master switch to the ARM position do

A
  • 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
25
Q

how is the standby hydraulic system automatically activated

A
  • 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
26
Q

when the automatic operation of the standby hydraulics is initiated what happens to the system

A
  • 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”
27
Q

what happens if a leak occurs in the standby system

A
  • 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
28
Q

what could cause variations in HYD QTY during normal operations

A
  • system becomes pressurized after engine start
  • raising or lowering the landing gear or leading edge devices
  • cold soaking during long periods of cruise
29
Q

what can cause hydraulic foaming

A

lack of reservoir pressure

30
Q

how can foaming be recognised

A
  • pressure fluctuations and blinking of “LOW PRESSURE”
  • MC + ‘HYD’ momentarily illuminate
31
Q

electric pump “OVERHEAT” light

A
  • hydraulic fluid used to cool and lubricate the pumps has overheated
  • pump itself has overheated
32
Q

“LOW PRESSURE” lights

A
  • output pressure of related pump is low (when engine fire switch is pulled = inhibited)
33
Q

electric hydraulic pump switch
- ON
- OFF

A
  • ON = powers associated electric hydraulic pump
  • OFF = removes power from associated electric hydraulic pump
34
Q

engine hydraulic pump switch:
- ON
- OFF

A
  • 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
35
Q

when does the ‘RF’ symbol on the HYD QTY indicator appear

A

qty < 76%
- on the ground AND both engines shutdown; OR
- after landing with flaps up during taxi-in

36
Q

FLT CONTROL switches (A AND B):
- ON
- OFF
- STBY RUD

A

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

37
Q

FLT CONTROL “LOW PRESSURE” lights

A
  • low hydraulic pressure to aileron, rudder and elevator
  • deactivated when associated flight control switch = STBY RUD + standby rudder shutoff valve open
38
Q

STANDBY HYD “LOW QUANTITY” light

A
  • low quantity in standby reservoir
  • always armed
39
Q

STANDBY HYD “LOW PRESSURE” light

A
  • output pressure of the standby electric pump is low
  • armed only when standby pump operating (by manual or automatic activation)
40
Q

STANDBY HYD “STBY RUD ON” light

A

when the standby hydraulic system is commanded on to pressurize the standby rudder power control unit

41
Q

ALTERNATE FLAPS master switch:
- OFF
- ARM

A
  • OFF = normal operating position
  • ARM:
    • closes trailing edge flap bypass valve
    • activates the standby electric pump
    • arms the alternate flaps position switch

B737 (10 decks)

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