Hydraulics

Question 1

How many Hydraulic systems are installed on the aircraft?

Answer 1

• 3 independent systems (HYD1 | HYD 2 | HYD 3)

Question 2

What systems use hydraulic power?

Answer 2

• Flight controls, Spoilers, Landing gear, Nose wheel steering, Wheel brakes,
  thrust reversers

Question 3

Can hydraulic fluid be transferred between each system?

Answer 3

• NO

Question 4

How many Hydraulic Pumps are on the aircraft?

Answer 4

• 6 total
• 2 EDP’s (Engine Driven Pumps)
• 4 ACMP’s (AC Motor Pumps)

Question 5

What is the purpose of the Accumulator?

Answer 5

• Helps to maintain constant pressure by covering transient demands
• Helps to avoid pump cavitation
• Provides a backup source of hydraulic energy or pressure

Question 6

When will ACMP 1 or 2 automatically activate with both Engines running?

Answer 6

• Ground
  i) Flaps > 0
  ii) TL set to T/O
  iii) Wheelspeed > 50 kts
• Flight
  i) Engine failure or EDP failure
  ii) Flaps > 0

Question 7

What are some important items controlled by HYD 2 system?

Answer 7

• Landing Gear, Nosewheel Steering, Inboard Brakes

Question 8

What is the PTU?

Answer 8

• Power Transfer Unit
• Mechanical pump that uses HYD 1 power to mechanically provide HYD 2
  pressure

Question 9

What is the primary purpose of the PTU?

Answer 9

• To allow landing gear retraction and extension in the event of an engine 2 or
  EDP 2 failure

Question 10

When will the PTU automatically activate?

Answer 10

• During takeoff and landing if the engine 2 or EDP 2 fails.
• The PTU will be started if:
  i) Flaps not set to zero or LG not up and locked;
  ii) EDP 1 not failed;
  iii) Hydraulic reservoir 2 quantity above 12%

Question 11

How is S.E. Taxi possible on ENG1 if Nosewheel Steering is on HYD 2?

Answer 11

• ACMP 2 will activate if engine 1 is running and the parking brake is released.
• Parking brake set after taxi, pump continues running for 6 minutes.

Question 12

What is the primary purpose of HYD 3 system?

Answer 12

• Back-up for the flight controls.

Question 13

HYD ACMP 3A & B pump switch(s) are labeled ON & AUTO because?

Answer 13

• HYD ACMP 3A pump is primary and has no automation

- HYD ACMP 3B pump is a back-up and automatically activates if ACMP 3A fails

Question 14

What, if any, HYD ACMP will function if the RAT is the only power source?

Answer 14

• HYD ACMP 3A only

Question 15

In an electrical emergency what provides hydraulic pressure to flight controls until
the RAT comes online?

Answer 15

• HYD 3 accumulator

- After 8 seconds the RAT will power ACMP 3A

Question 16

In an electrical emergency can HYD 3 system power requirements overload the
RAT?

Answer 16

• No. Because, a flow limiter valve is used to reduce flow and limits pump electrical
  power draw to prevent a RAT stall.

Question 17

What is the hydraulic pressure during normal operation of the EDP(s)?

Answer 17

• 3000 psi

Question 18

Which hydraulic pump cannot be deferred? Why?

Answer 18

• Hydraulic Pump 3a

- Only one powered by AC ESS BUS during electrical emergency

Question 19

What does the hydraulic shutoff button do when pressed on the overhead panel?

Answer 19

• Closes the Shutoff Valve. Isolates fluid from the Pump but does not shut it down.

Question 20

What overheat protection is provided for the hydraulic system?

Answer 20

• 100°C generates a High Temperature EICAS Caution message.
• 125°C shutoff valve will automatically actuate.
• 145°C generates a Hydraulic Overheat EICAS Warning message