Hydraulics Flashcards
Possible causes of the FAULT light illuminating in the engine hydraulic pump pb:
- Low pump output pressure
- Low reservoir quantity
- Reservoir overheat
- Reservoir low air pressure
Prior to engine start, when a cargo door selector is placed in either the open or closed position, the yellow electric pump activates but will only power:
- The cargo doors
- The alternate brake system
- The engine two thrust reverser
With AC power available, when does the Blue electric pump operate?
- On the ground when at least one engine is running
- Continuously in flight, even if both engines are shut down
The PTU pb FAULT light does not indicate a fault with the PTU itself; instead, is illuminates in response to an abnormal in either the Green or Yellow system reservoirs due to:
- Overheat
- Low air pressure
- Fluid loss
The fault light in the PTU pb helps to direct the flight crew to turn off the PTU.
The PTU is automatically inhibited when:
- The Yellow system’s electric pump is running because of cargo door operation, as well as 40 seconds after its use (prevents Green pressurization)
- During engine start, when the ENG MASTER switches are in opposing position AND either the nosewheel steering is disconnected, OR the parking brake is on
The PTU performs a momentary self-test during the second engine start.
When does the RAT deploy automatically?
The RAT deploys automatically in flight if there is a loss of AC buses 1 & 2.
The RAT does not deploy automatically in response to a hydraulic system failure.
What is the purpose of the guarded RAT MAN ON pb?
The guarded RAT MAN ON pb on the HYD panel allows you to manually extend the RAT to pressurize the Blue system without causing the emergency generator to come on line.
What is the purpose of the hydraulic accumulators?
Prevents/absorbs spikes in the hydraulic system as well as holds pressure.
How are the hydraulic fire shutoff valves closed?
The Flight Crew can close it by pushing the ENG 1(2) FIRE pushbutton.
What are the purpose of the hydraulic priority valves?
Priority valves cut off hydraulic power to heavy load users if hydraulic pressure in a system gets low.
How do the hydraulic reservoirs maintain pressurization?
Normally, HP bleed air from engine 1 pressurizes the hydraulic reservoirs automatically. If the bleed air pressure is too low, the system takes bleed air pressure from the crossbleed duct. The systems maintain a high enough pressure to prevent their pumps from cavitating.
There is a check valve on either side of the X BLEED VALVE followed by a filter that feeds to all 3 reservoirs.
When does the Blue hydraulic pump operate?
If AC power is available, the electric pump operates:
In flight
On the ground, if at least one engine is running
The pump will also operate when the crew has pressed the BLUE PUMP OVRD pushbutton on the maintenance panel.
When are the WTBs activated?
Wingtip brakes (WTBs), activated in case of asymmetry, mechanism overspeed, symmetrical runaway, or uncommanded movement of the surfaces. They cannot be released in flight. They use blue and green hydraulic power for the slats and for the right wing flaps, and blue and yellow hydraulic power for the left wing flaps.
Can the flight crew dispatch with an inoperative Blue Electric Pump?
No, but the Yellow Electric Pump is deferrable, so the two can be interchanged if necessary.
When arriving at the gate, what would the issue be if the Yellow Electric Pump was inoperative?
An increase in physical labor for the ground crew as they would need to use the hand pump.
