Hydraulics

Question 1

What does the PTU do?

Answer 1

Power Transfer Unit. Assists the landing gear extension and retraction if an engine 2 or EDP2 failure happens. Transfers flow rate (not fluid!) from EDP1 mechanically to the hydraulic fluid in system 2 (PTU).

Question 2

What is the pump unloader valve/flow limiter valve and on what hydraulic system can it be found?

Answer 2

This is used in an electrical emergency to avoid overload in the RAT. Hydraulic system 3.

Question 3

How does the emergency/parking brake accumulator work?

Answer 3

It stores hydraulic pressure from systems 1 & 2 for the sole use of the Emergency/Parking brake. If hydraulic system 1 & 2 become depressurized, provides enough power for 6 brake applications.

Question 4

What does the PTU need to work?

Answer 4

Requires EDP1 to work and system 2 reservoir to be at least 12%.

Question 5

When will the PTU come on whilst in AUTO?

Answer 5

ON when flaps not 0 or landing gear not up and locked, and EDP2 fails, or engine 2 fails.

Question 6

When does Electric hydraulic pump 1 come on in AUTO, and when does Electric Hydraulic Pump 2 come on in AUTO?

Answer 6

T/O: flaps > 0 and 50 knots GS OR thrust levers in TOGA.
Flight: flaps > 0, or EDP fail, or engine failure.
Same with Electric Hydraulic Pump 2, but also SE taxi: if only engine 1 is running, and parking brake is released or set within the last 6 minutes.

Question 7

What hydraulic system powers the inboard brakes?

Why is this important to know?

Answer 7

Hydraulic system 2.
This is important because when SE taxi on Eng 1; hydraulic system 1 and hydraulic system 2 will turn on.
SE taxi on Eng 2; it will turn on Hydraulic system 2, but not system 1. In this case you need to turn on pump 1 to get both inboard and outboard brakes.

Question 8

Does the Emer/Parking Brake have a dedicated accumulator?

Answer 8

Yes. It stores pressure from system 1 and system 2 for the SOLE use of the Emer/Parking brake. (not the brake pedals)

Question 9

If system 1 and 2 are depressurized, will the Emer/Parking brake still work if the accumulator has adequate pressure?

Answer 9

Yes, the accumulator provides enough pressure for 6 emergency or parking brake applications (not brake pedal applications).