Hydraulics

Question 1

When positioning either FLT CONTROL switch to STANDBY RUD, what happens?

Answer 1

• Engages motor driven pump for standby system
• Isolates Aileron, Elevator, and Rudder
• Opens the standby rudder shutoff valve
• Powers Thrust Reverser and Rudder
• Extinguishes LOW PRESSURE for appropriate system (when stanby SOV opens)
• Arms STANDBY HYD LOW PRESSURE light for Standby system
• STBY RUD ON illuminates which results in FLT CONT and Master Caution

Question 2

Automatic activation of standby hydraulic system occurs when?

Answer 2

Failure of A and or B system when the flaps are extended and…
- Airborne OR
- Wheel Speed is greater than 60 kts

Force Flight Monitor trips

Question 3

What does the standby hyd system operate?

Answer 3

Rudder (+ YD), Thrust Reversers, & Leading Edge devices via manual flap extension,

Question 4

Which reservoir is what

Answer 4

Question 5

Does the Landing Gear Transfer System literally transfer fluid?

Does the PTU?

Answer 5

LTV - Yes. A limited one way transfer to raise the gear at a normal rate. It is activated when:
* #1 N1 < 50%
* Gear selected UP
* Any main gear is not up

PTU - No.

Question 6

What are the hydraulic systems of the 737?

Answer 6

• system A
• system B,
• and a standby system.
• Hydraulic system(s) provide power to the autopilot, flight controls, landing gear, thrust reversers, and tail skid.

Question 7

How are hydraulic reservoirs pressurized?

Answer 7

Systems A and B: bleed air

Standby system is pressurized and serviced through system B by a fill line.

Pressurization of the systems ensures positive fluid flow to all the hydraulic pumps.

Question 8

How are hydraulic systems quantity and pressure indications indicated on the MDS?

Answer 8

On the inboard Display Unit after selecting SYS on the MFD panel. A second selection of the SYS switch will remove it from the respective DU.

Question 9

What does an RF on the HYDRAULIC indicator indicate and when is it valid?

Answer 9

The reservoir is below 76% and requires servicing.

The RF indication is only valid when:
* On the ground with both engines shut down, OR
* After landing during taxi-in with the Flaps UP.

Question 10

How does flap operation affect hydraulic fluid quantity indications?

Answer 10

Extension of the leading edge devices may result in up to 20% drop in indicated quantity.

Question 11

What is the normal pressure of hydraulic systems A & B?

Answer 11

The normal pressurization for system A and B is 3000 ± 200 psi. Maximum system pressure is 3500 psi. Without hydraulic pump operation, pressurization can expect to be less than 100 psi.

Question 12

When does the STANDBY HYD LOW QUANTITY light illuminate?

Answer 12

Indicates the standby hydraulic system has less than 50% quantity in the reservoir.

Question 13

Which precaution(s) should be taken when turning on the electric hydraulic pumps?

Answer 13

Placing both ELEC HYD PUMPS switches to ON simultaneously may create an amperage surge, resulting in hydraulic pump motor circuit breakers tripping in the E/E compartment. Staggering switch selection ON avoids this possibility.

Question 14

What does moving a FLT CONTROL switch to STBY RUD do?

Answer 14

• Activates the standby electric motor-driven pump
• Opens the standby rudder shutoff valve
• Closes the flight control shutoff valve, shutting off the related hydraulic system pressure to ailerons, elevators, and rudder.
• Deactivates the related FLT CONTROL LOW PRESSURE light when the standby rudder shutoff valve opens
• Arms the STANDBY HYD LOW PRESSURE light
• Illuminates the STBY RUD ON light which illuminates the FLT CONT System Annunciator and MASTER CAUTION lights.
• Allows the standby system to power the rudder and thrust reversers

Memory aid:
Manual: 1 pump, 2 valves, powers rudder and T/R’s, 6 lights (1 off, 6 on)

Question 15

What causes the automatic operation of the standby hydraulic system?

Answer 15

Automatic activation is initiated when the FLT CONTROL switches are positioned ON (normal operating position) with a loss of system A and/or B and one of the following conditions occur:

• Flaps extended, airborne
• Flaps extended, wheel speed greater than 60 kts
• Automatic activation also occurs any time the main rudder Power Control Unit (PCU) Force Fight Monitor (FFM) trips (for more information, see 9.010, Force Fight Monitor).

Question 16

What does automatic operation of the standby hydraulic system activate?

Answer 16

• Activates the standby electric motor-driven pump
• Opens the standby rudder shutoff valve
• Allows the standby system to power the rudder and thrust reversers
• Illuminates the STBY RUD ON light and the FLT CONTROL System Annunciator and MASTER CAUTION lights.

Question 17

What is the purpose of the PTU?

Answer 17

Provides hydraulic system B fluid at a flow rate and pressure sufficient to provide normal rates of operation of the leading edge devices (including autoslats) in the event the hydraulic system B EDP output pressure is less than 2350 psi.

Question 18

What fluid percentage does the standpipe in the system A reservoir preserve in the event of a leak?

Answer 18

With fluid level at the top of the standpipe, the reservoir quantity displayed indicates approximately 20% full.

Question 19

What fluid percentage does the standpipe in the system B reservoir preserve in the event of a leak?

Answer 19

Approximately Zero, but still with fluid level at the top of the standpipe, fluid remaining in the system B reservoir is sufficient for PTU operation.

Question 20

With 0% indicated on the system B quantity indicator, can the PTU still operate?

Answer 20

If a leak develops in either pump, line, or component of system B, the quantity decreases until it indicates approximately zero and system B pressure is lost; however, with fluid level at the top of the standpipe, fluid remaining in the system B reservoir is sufficient for PTU operation.

Question 21

How does a leak in the standby hydraulic reservoir affect the system B quantity?

Answer 21

If a leak occurs in the standby system, the standby reservoir quantity decreases to zero.
System B continues to operate normally; however, the system B reservoir fluid level indication decreases and stabilizes at approximately 70% full.

Question 22

What components of system A are unique to that system?

Answer 22

Ground Spoilers.
Alternate Brakes.
No. 1 Thrust Reverser.
Autopilot A.
Normal Nose Wheel Steering.
Landing Gear.
Power Transfer Unit (PTU).
Tail Skid (900ER and MAX)

Bonus variant answers;
Freighters - Main Cargo Door on System A,
900ER is the only variant besides the MAX with Tailskid hydraulic power.

Question 23

What components of system B are unique to that system?

Answer 23

Leading Edge Flaps and Slats.
Normal Brakes. Brake Accumulator.
No. 2 Thrust Reverser.
Autopilot B.
Alternate Nose Wheel Steering.
Landing Gear Transfer Unit.
Autoslats.
Yaw Damper.
Trailing Edge Flaps.

Question 24

Which hydraulic system(s) is used to raise and lower the landing gear normally?

Answer 24

Hydraulic power for retraction, extension, and nose wheel steering is normally supplied by hydraulic system A. A manual landing gear extension system and an alternate source of hydraulic power (system B) for nosewheel steering are also provided.

Question 25

Explain the Landing Gear Transfer Valve:

Answer 25

Provides pressure to the landing gear using system B **pressure and fluid** in the event system A Engine Driven Pump is lost. Allows a limited one way transfer to raise the gear at a normal rate. It is activated when: * #1 N1 < 50% * Gear selected UP * Any main gear is not up

Question 26

The standby hydraulic system can be activated manually or automatically, how does the system activation change for either?

Answer 26

**BOTH** - Activate the Standby Electric Motor-Driven Pump - Open the Standby Rudder Shutoff Valve - Allow the Standby System to power rudder and thrust reversers - Illuminate the STBY RUD ON annunciator (which illuminates FLT CONTROL and MASTER CAUTION lights. **In addition, Manual activation:** - Closes the flight control shutoff valve, shutting off the related hydraulic system pressure to ailerons, elevators, and rudder. - Deactivates the FLT CONTROL LOW PRESSURE light when the rudder shutoff valve opens. - Arms the STANDBY HYD LOW PRESSURE light.