Hydraulics

Question 1

How many hydraulic systems are on the airplane?

Answer 1

3 independent systems.
HYD 1, 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, the systems are independent of each other

Question 4

How many hydraulic pumps are on the airplane?

Answer 4

7 total:
2 EDP’s (Engine Driven Pumps)
4 ACMPs (AC Motor Pumps)
1 PTU

Question 5

What are the basic components of the hydraulic systems?

Answer 5

• Reservoir
• Pumps (2 engine driven, 3 AC electric)
• Accumulator (3,000 psi)

Question 6

What is the purpose of the accumulator?

Answer 6

Helps to maintain constant pressure (3,000 psi) by covering transient demands (shock absorption).

Helps to avoid pump cavitation.

Question 7

When will ACMP 1 or 2 automatically activate?

Answer 7

Ground:
Flaps greater than 0 and TL set to TOGA, or Groundspeed greater than 50 knots. (Remains on for 60 seconds after TL at TOGA).

Flight:
Engine failure or EDP failure.
Flaps greater than 0. (Remains on for 60 seconds after landing)

Question 8

What are the important items controlled by HYD 2 system?

Answer 8

Landing gear
Nose-wheel steering
Inboard brakes

Question 9

What is the PTU?

Answer 9

Power Transfer Unit
Mechanical pump that uses HYD 1 power to provide HYD 2 pressure. (need a minimum of 12% fluid quantity in System 2)

Question 10

What is the primary purpose of the PTU?

Answer 10

To allow landing gear retraction (for climb performance) and extension in the event of an ENGINE 2 or EDP 2 failure. (PTU not activated on ground)

Question 11

When will the PTU automatically activate?

Answer 11

During takeoff and landing with flaps greater than 0 IF:
- Engine 2 fails, or EDP 2 fails
- Fluid quantity in System 2 greater than or equal to 12% (EDP #1 must be operational)

Question 12

How is the single engine taxi possible if nose wheel steering is on HYD 2?

Answer 12

Releasing the parking brake activates ACMP 2.

Question 13

What is the primary purpose of HYD 3 system?

Answer 13

Back-up for the flight controls:
Elevator - Right hand OB actuator
Rudder - lower actuator
Ailerons - Left and Right OB actuators

Question 14

Why does HYD ACMP 3A pump switch have an ON position and HYD ACMP 3B have an AUTO position?

Answer 14

HYD ACMP 3A pump is primary and has no automation (either ON or OFF selected by crew)

HYD ACMP 3B pump is a back-up and (Auto)matically (logic) activates if ACMP 3A fails. If selected ON, pump operates continually.

Question 15

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

Answer 15

HYD ACMP 3A only. (Powered by the AC ESS Bus)
During an Electrical Emergency it powers the elevator, rudder, and ailerons in Direct Mode.

Question 16

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

Answer 16

HYD 3 Accumulator.
(3,000 psi stored pressure)
After 8 seconds the RAT will power ACMP 3A through the AC ESS Bus

Question 17

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

Answer 17

No. A flow limiter valve (FLV) is used to reduce flow and limits pump electrical power draw to prevent a RAT stall.

PUV - Pump Unloader Valve reduces pump torque.

These 2 valves are used only during an Electrical Emergency and only on HYD sys 3.