B737 Hydraulics Flashcards
For which system powers which components, refer to my 737 deck
What’s the normal pressure for the hydraulic brake accumulator?
3000PSI
What are the conditions that cause the landing gear transfer unit to operate?
- airborne
- No. 1 engine RPM drops below a limit value
- LANDING GEAR lever is positioned UP
- either main landing gear is not up and locked.
(will use hydraulic system B to rause gear instead of A)
Is antiskid system available if all hydraulic pressure is lost?
Yes
What does an amber OVERHEAT mean above a electric hydraulic pump switch mean?
Hydraulic fluid used to cool and lubricate the corresponding electric motor driven pump has overheated or the pump itself has overheated.
What position should the engine driven hydraulic pump switches be at engine shutdown?
ON
What is the maximum hydraulic pressure of system A or B?
3500PSI
RF will illuminate next to hydraulic system A or B quantity when it is below what %?
It is only valid in certain circumstances - what are they?
76%
(refill)
Valid only when airplane is on ground with both engines shutdown or after landing with flaps up during taxi–in.
The standby hydraulic system is connected to which main hydraulic system?
B
What happens when you switch off an engine driven hydraulic pump?
Isolates fluid flow from system components but pump rotates as long as engine is operating.
If a leak develops in the electric motor driven pump of hydraulic system A or its related lines the reservoir will drop to what quantity?
Is system pressure maintained?
Zero, all pressure lost
If there is a leak in the engine driven pump of hydraulic system B or its related lines the reservoir will drop to approximately what quantity?
Is system pressure maintained?
Zero - all system pressure lost
(Still sufficient fluid for PTU)
If there is a leak in the electric motor driven pump of hydraulic system B or its related lines the reservoir will drop to approximately what quantity?
Is system pressure maintained?
Zero - all system pressure lost
(Still sufficient fluid for PTU)
Does a leak in hydraulic system B affect the operation of the standby hydraulic system?
No
To which main hydraulic system is the standby hydraulic system connected?
B
A hydraulic LOW PRESS light will illuminate when the hydraulic pressure drops below what psi?
1300 psi
Summarise what the PTU does
- supplies additional volume of hydraulic fluid to operate auto slats and leading edge devices at normal rate if system B pressure is low (engine no.2 EDP pressure lost).
What conditions cause the PTU to operate?
- airborne
- system B engine driven pump falls below 2350PSI for more than 0.5s
- flaps not up
- (some a/c flaps less than 15 but not up)
Is there fluid transfer between hydraulic system A and B when the PTU is operating?
No - system A pressure is used to power a hydraulic motor driven pump which pressurises system B hydraulic fluid.
If a leak occurs in the standby hydraulic system, the standby reservoir depletes to zero. What happens to system B quantity?
Decreases to around 72%.
What happens if the Force Fight Monitor detects opposing pressure between A and B rudder actuators?
- Standby hydraulic pump turned on
- Standby rudder shut off valve open to pressurize the standby rudder PCU (and Thrust Reversers)
- STBY RUD ON illuminates with Master Caution FLT CONT
What conditions cause the standby hydraulic system to automatically operate?
- loss of hyd. system A or B, and
- flaps extended, and
- airborne, or wheel speed greater than 60kts, and
- FLT CONTROL switch A or B Hydraulic system ON
OR - the main PCU Force Fight Monitor trips
What is the brake accumulator pre-charge pressure?
1000PSI
Autobrake requires which hydraulic system to be operating?
B
The HYD Brake Pressure indicator reads zero, but both hydraulic system pressures are normal, what is this telling you?
The nitrogen precharge in the brake accumulator has leaked out, accumulator braking is not available but normal braking is unaffected.
