Hydraulic System

Question 1

Which is the “heavy” system on each type? What makes it “heavy”?

Answer 1

757 - Left hydraulic system
767 - Center hydraulic system

The “heavy” system has the flaps/slats and gear retraction/extension - these are heavy hydraulic load items. Items on the heavy system = FANG (Flaps/slats, Alternate brakes, Nose wheel steering, Gear). The heavy system also has the ER items: HDG and tail skid (767 only).

Question 2

Which hydraulic system has the normal brakes?

Answer 2

Right system

Question 3

What is the Pitch Enhancement System (PES)?

Answer 3

Alternate method for moving the stab trim (767 only) using Right hydraulics if the Left and Center systems fail. Uses Left system standpipe fluid. It’s like a PTU for just the stab trim.

Question 4

Which systems can use reservoir below-standpipe fluid in case of a hydraulic leak?

Answer 4

757 - PTU (Left) / Reserve Brakes (Right) / RAT (Center)

7676 - Reserve Brakes and Steering (Center)

Question 5

Which hydraulic items use all three systems (1 primary and 2 backups)?

Answer 5

SEAR - Spoilers, Elevator, Autopilot servos, Rudder

Question 6

Which hydraulic items use two systems (1 primary and 1 backup)?

Answer 6

YES - Yaw damper, Elevator feel, Stab trim

*Note: the Pitch Enhancement System (767 only) serves as 3rd backup to the stab trim (right hyd power, but left hyd fluid)

Question 7

Minimum speed for RAT to produce adequate pressure for flight controls?

Answer 7

130 knots

Question 8

Hydraulic items powered by the RAT?

Answer 8

Flight controls only on the center system. SAFETY: Spoilers, Autopilot servos, Flight controls primary (ailerons, elevators, rudder), Elevator feel, Trim for stab, Yaw damper.

Question 9

How does pulling the ENG FIRE switch affect the hydraulic system?

Answer 9

Depressurizes and shuts off fluid to the engine driven hydraulic pump

Question 10

L & R electric hydraulic pumps - what is the difference between the 757 and 767?

Answer 10

757 - full-time pumps

767 - on-demand (low pressure, high demand (i.e. flaps/gear), and HDG operating)

Question 11

Pressing the RESERVE BRAKES / Reserve BKS & STRG switch does what 3 things?

Answer 11

1) Activates electric hydraulic pump (757 right pump / 767 #1 center pump)
2) Isolates the brakes and pump from the rest of the hydraulic system
3) Illuminates ON light

Question 12

What’s the difference in Reserve Brakes between the 757 and 767?

Answer 12

757 - Anti-skid for individual wheels

767 - Anti-skid for paired wheels (same axle)

Question 13

What does it take to get Accumulator brakes?

Answer 13

Loss of hydraulic system pressure (normal, alternate, and reserve) - accumulator isolation valve opens.

The accumulator isolation valve closes with normal brake system pressure

Question 14

What is the Power Transfer Unit (PTU) and what hydraulic items does it power?

Answer 14

PTU (757 only) is a hydraulically powered hydraulic pump that uses hydraulic pressure from the right system to drive a pump that uses fluid in the left system to power Nose wheel steering, Flaps/slats, Landing gear (NFL) + HDG on ER models

Question 15

When does the RAT deploy automatically?

Answer 15

In flight when both engines N2 drops to 50% or less

Question 16

Left demand HYD pump in AUTO is inhibited when?

Answer 16

When there is only a single generator source

Question 17

(767) When is the Right HYD demand pump always commanded on and why?

Answer 17

Right HYD demand pump commanded ON when flaps are in the takeoff position to ensure brake pressure for RTO

Question 18

PRESS light in each HYD pump switch - what does it indicate?

Answer 18

That pressure from that pump was requested but not given

Question 19

OVHT light in each HYD pump switch - what does it indicate?

Answer 19

Fluid temp for exiting that pump is hot