parking brake is part of the hydraulic system..
so if the parking brake will stuck?!
automatically....there is a problem in a hydraulic system
[EG: 747-400 hydraulic system #4 or A320 yellow system]
so it is possible to happend but it is a very rare situation..
before the a/c released after it's maintenance check
[A,C and D checks] theres lot of checks will be perfomed BITE test, system check, OPC[operational checks] to ensure the a/c is airworthy and ready for flight...
if a hydraulic problem detected on the ground...automatically it will indicated at the EICAS/ECAM page..and the a/c will be grounded for safety....
either drop-down of pressure or faulty sensor indicator or other related problems occurred in hydraulic system...
as per AMM [aircraft maintenance manual]
here are the full info about parking brakes...
A320
PARKING/ULTIMATE EMERGENCY BRAKING - DESCRIPTION AND OPERATION
1 . General
**ON A/C 001-002,
(Ref. Fig. 001)
When you set the PARK BRK control switch to the ON position, this
deactivates the other modes and supplies the brakes with Yellow high
pressure. If Yellow high pressure is not available the brake Yellow pressure
accumulator supplies power limited at 145 bar (2103.0466 psi) to the brakes.
The accumulator has sufficient capacity to hold the brakes on for a minimum
time of twelve hours. The TO CONFIG warning light (on the ECAM control
panel) reminds the crew to release the parking brake when the engine is at
full throttle.
R **ON A/C 001-003, 101-199, 201-203, 251-299,
R Post SB 32-1201 For A/C 001-002,
When you set the PARK BRK control switch to the ON position, this
deactivates the other modes and supplies the brakes with Yellow high
pressure. If Yellow high pressure is not available the brake Yellow pressure
accumulator supplies power limited at 145 bar (2103.0466 psi) to the brakes.
If the parking brake pressure decreases to less than 35 bar (507.6319 psi)
when the PARK BRK is in ON position, the system reactivates the Normal
Braking mode automatically.
The accumulator has sufficient capacity to hold the brakes on for a minimum
time of twelve hours. The TO CONFIG warning light (on the ECAM control
panel) reminds the crew to release the parking brake when the engine is at
full throttle.
PARKING/ULTIMATE EMERGENCY BRAKING - DESCRIPTION AND OPERATION
1 . General
(Ref. Fig. 001)
The parking/ultimate emergency braking system is an electrohydraulic system.
Its primary function is to prevent movement of the aircraft when it is
parked. It can also be used in an emergency mode to stop the aircraft if
control in all the other braking modes
(Ref. 32-42-00), (Ref. 32-43-00) and (Ref. 32-44-00)
is not available. Use of the parking brake overrides all
other braking systems when the parking brake pressure is available.
The system gets its hydraulic power supply from the accumulator of the
Alternate Braking Without Anti Skid system (Ref. 32-44-00) or the Yellow
Main Hydraulic Power system (Ref. 29-13-00). The accumulator has sufficient
capacity to hold the brakes on for a minimum time of twelve hours.
When the selector switch PARK BRK in the cockpit is set to ON, it sends an
electrical supply to the electrohydraulic park brake control valve 102GG.
This valve controls the supply of hydraulic pressure to the MLG brake
pistons of the Alternate Braking with Anti Skid system (Ref. 32-43-00). The
hydraulic pressure available to the system (accumulator or Yellow system)
and the brake pressure supplied to the MLG is shown on a triple pressure
indicator (Ref. 32-44-00) in the cockpit.
If the Normal braking system is available and, if the pedals are depressed
when the PARK BRK is ON and the pressure commanded by the pedal deflection
exceeds the pressure delivered by the Park brake system, the Normal system
will send a complement of pressure to the Normal set of pistons to reach the
commanded value.
3 . System Description
The parking/ultimate emergency brake system has these components:
- the park brake control switch 73GG
- the park brake control valve 102GG
The selector switch is a four-pole, two position (OFF/ON) switch that sends
the power supplies to the two electrohydraulic control valves in the system.
The system has two independent electrical circuits each with a different
power supply (service bus and hot bus). Usually the circuits are energized
at the same time. Each circuit can operate the park brake control valve
102GG the other is not available.
The HP alternate brake manifold assembly 3016GM connects the hydraulic power
supply lines from the Yellow system and the accumulator (Ref. 32-44-00) to
the park brake control valve 102GG.
The HP alternate brake manifold assembly 3016GM includes a pressure relief
valve. If the pressure in the system increases to more than a specified
quantity (because of changes in temperature), the pressure relief valve
connects the supply to the return. A manual depressurization switch lets
maintenance personnel open the relief valve to release the accumulator
pressure (for system servicing).
The manifold has a check valve to prevent the flow of fluid from the
accumulator to the Yellow supply line when the Yellow line is not
pressurized. A pressure transducer 3068GN (Ref. 32-44-00) attached to the
manifold transmits the system pressure data to the triple pressure indicator
60GG (Ref. 32-44-00) and to the ABCU (Ref. 32-43-00).
The park brake selector valves is an electrohydraulic valve . The park brake
control valve has two electric motors that can open or close the valve. When
the valve is energized (open) it:
- reduces the pressure of the available hydraulic supply to 175 bar (2500
psi)
- sends this hydraulic supply to the alternate brake manifold assemblies
(Ref. 32-43-00) of the MLG
The park brake control valve also has an interface with the electrical
de-activation box 5GC of the Nose Wheel Steering (N/WS) system (Ref.
32-51-00). The de-activation box includes a light that lets maintenance
personnel see when the parking brake is set to ON.
----------------------------------------------------------------------
747-400
PARKING BRAKE SYSTEM - DESCRIPTION AND OPERATION
1 . General
A. A parking brake system is provided to permit setting the brakes during
parking and mooring. The system consists of a parking brake lever on the
control stand which operates an electrical switch and an electrical motor
operated parking brake module. The parking brake operates on the normal
brake system only and can be set only when hydrualic system 4 is
pressurized.
B. The parking brakes may be set by either the captain or the first officer.
A PARKING BRAKE SET indication will come into view on EICAS when the
parking brake is set. Setting the parking brake enables the erase
circuit in the voice recorder system, AMM 23-71-00/201.
C. AIRPLANES WITH A REMOTE BRAKE INDICATOR LIGHT;
A BRAKE ON light on the P37 Nose-Wheel-Well-Control panel (on the nose
gear above the steering collar) will also come on when the parking brake
is set.
D. Parking brake indication and brake pressure indication may be transfered
to the hot battery bus to remain operational when the airplane is being
towed.
E. The parking brake indication and brake pressure indication can also be
transferred to the ground handling bus so it operates when the airplane
is towed.
2 . Parking Brake Lever and Linkage (Fig. 1).
A. The parking brake lever is located on the left side of the flight deck
center console. It is connected to the parking brake linkage which
consists of shafts, levers, connecting rods, a tube assembly and pawls.
When one of the flight crew push the brake pedals to the stops and pull
the parking brake lever, the pawls in the linkage are rotated to engage a
shaft on the brake pedal bell crank. This holds the brakes in the
applied position.
3 . Parking Brake Indication (Fig. 2)
A. Parking brake indication is shown on the EICAS on the P2 panel. When the
parking brake lever is pulled, the movement of the linkage sets a micro
switch. This passes power from the PARK BRAKE circuit breaker on the P6
panel to the close fields of the electric motor on the parking brake
module. When the electric motor has cycled to the closed position, power
and ground are provided to turn on the Parking-Brake-Valve-Closed Relay.
When the relay switches it establishes a path from the electrical
interface units (EIUs) to ground, and this permits the PARKING BRAKE SET
indication to appear on EICAS.
B. AIRPLANES WITH A REMOTE BRAKE INDICATOR LIGHT;
When the relay switches, it also provides a ground through the S313
Parking Brake Lever Switch to turn on the BRAKE ON light (L1541) on the
P37 panel.
C. When the airplane is being towed, parking brake indication may be
provided from the hot battery bus. This is done by setting the STBY
power switch to off and the TOWING BAT PWR switch on the overhead panel
to BAT. 28 vdc power from the battery bus can then operate parking brake
indication. DC Battery bus power is also routed through a static towing
inverter to provide an AC signal to operate the brake pressure
transmitter at the brake accumulator. This allows the brake accumulator
pressure to be monitored on the HYD BRAKE PRESS gage on the flight deck.
D. When the airplane is being towed, parking brake indication can also be
supplied from the ground handling bus. This is done by setting the STBY
power switch to OFF and the TOWING POWER BACKUP switch on the overhead
panel to ENABLE. 28 vdc power from the ground handling bus can then
operate the parking brake indication.
E. When the parking brake is released the linkage moves to the off position
which permits the micro switch to return to off. This passes power form
the PARK BRAKE circuit breaker to the open fields of the electric motor
in the parking brake module. When the electric motor has cycled to off,
power and ground are moved from the Parking-Brake-Valve-Closed relay to
Parking-Brake-Valve-Open Relay. When the Parking-Brake-Valve-Open relay
is set, a ground signal to the EIUs suppresses a fault indication on the
EICAS screen. If the electric motor in the Parking Brake Module fails to
cycle to the open position both relays will be relaxed producing no
ground signal to the EIUs. This will cause a PARKING BRAKE VALVE
indication to come into view on EICAS.
F. If the electric motor on the parking brake module fails to open when the
parking brake linkage is released, pressure will build up in the return
lines of the antiskid valves causing an antiskid malfunction. For this
reason the parking brake valve status is monitored by the antiskid
circuits in the Brake Control Unit. When the Parking-Brake-Lever Switch
is in the off position and the Parking-Brake-VAlve-Open Relay remains
off, a ground is removed from the parking-brake-logic input in the brake
control unit. This causes an ANTISKID OFF indication to come into view
on EICAS.
4 . Parking Brake Module and Thermal-Pressure-Relief Valve (Fig. 3)
A. The parking brake module prevents the brake accumulator from discharging
through the normal antiskid valves when the parking brake is set. It is
installed on the keel beam in the right-body-gear-wheel well and is
connected to the hydraulic system return lines from the normal antiskid
modules.
B. The Parking Brake Module contains an electric motor actuated cartridge
valve and a check valve. The motor can set the valve to one of two
positions called POS 1 and POS 2. In POS 1 the IN-A port is blocked and
the IN-B port is connected to the OUT port. In POS 2 the IN-A port and
the IN-B port are connected to the OUT port. The check valve is
installed in the OUT port to prevent backflow from the hydraulic system
return line.
(1) The electric-motor-actuated-cartridge valve is a three-way, two
position valve operated by an 18 - 30 vdc motor. When the actuator
is in position 1, the pressure and return ports of the valve are
blocked. When the actuator is in position 2, the pressure and
return ports are connected together. When the valve is in transit,
all ports are blocked.
(2) The electric motor contains two fields and two limit switches. One
field turns the motor in a counterclockwise direction to position 1,
and the other field turns the motor in a clockwise direction to
position 2. When the parking brake is set, power is applied to the
position 1 field, and the motor cycles all the way to position 1.
At position 1 a limit switch disconnects the position 1 field from
parking brake set circuit and connects the position 2 field to the
parking brake off circuit. When the parking brake is released the
position 2 field is powered and the motor turns clockwise to
position 2 where the limit switch disconnects the position 2 field
from the parking brake off circuit and connects the position 1 field
back to the parking brake on circuit.
C. A Thermal-Pressure-Relief valve is installed adjacent to the Parking
Brake Module and connects the IN-A port to the IN-B port. This protects
the brake system from pressure buildup which is caused by expansion when
a cold soaked airplane begins to warm. The valve opens and releases
fluid into the return lines when pressure in the brake lines exceeds 3400
psi. When pressure drops below 3100 psi the valve closes.
5 . Operation (Fig. 4)
A. Functional Description
(1) The parking brakes operate off the normal braking system. The
pressure source is the hydraulic brake accumulator which is
pressurized by hydraulic system 4.
(2) When the control pedals are pushed into the stops and the parking
brake lever is pulled, the linkage moves two pawls toward the brake
pedal bellcrank. The pawls engage lockpins on the bell crank and
hold the brake linkage in the applied position. The parking brake
linkage will not set unless both brake pedals are pushed to the
applied position.
(3) When the parking brake lever is pulled and the linkage operates a
switch that provides 28 vdc power to the electric motor in the
parking brake modle. The motor cycles the module to the closed
position. This blocks the normal antiskid valve return lines to
prevent the accumulator from discharging through the antiskid
valves.
(4) The pressure on the HYD BRAKE PRESS gauge can decrease quickly after
you set the parking brake and remove the hydraulic power. This is
because the antiskid surge accumulators fill with hydraulic fluid.
This condition is satisfactory if the pressure does not decrease to
less than 1700 psig.
(5) AIRPLANES WITH "BRAKE ON" LIGHT ON P37 PANEL;
With the parking brake set and the parking brake valve (V23) closed,
the parking brake lever switch also powers the Parking Brake Closed
Relay (R7514) to allow a PARKING BRAKE SET indication on EICAS, and
the BRAKE ON light on the P37 panel to come on. The relay will also
permit the flight deck voice recorder to be erased.
(6) AIRPLANES WITHOUT "BRAKE ON" LIGHT ON P37 PANEL;
With the parking brake set and the parking brake valve (V23) closed,
the parking brake lever switch also powers the Parking Brake Closed
Relay (R7514) to allow a PARKING BRAKE SET indication on EICAS. The
relay will also permit the flight deck voice recorder to be erased.
(7) The parking brake lever returns to its original (off) position
automatically when both brake pedals are fully depressed and then
released. The return lever operates the parking brake lever switch
to the off position. This cycles the parking brake module to the
open position which permits the flow of hydraulic fluid through the
normal antiskid modules to hydraulic system 4 return lines. This
permits the antiskid system to function. Brake pressure is released
through the brake metering valves.
(8) The parking brake module cycles to the open position the
Parking-Brake-Valve-Open Relay is energized. This suppresses the
PARKING BRAKE VALVE and the ANTISKID OFF message on EICAS.
B. Control
(1) Set the parking brake.
(a) Make sure that hydraulic system No. 4 is pressurized
(AMM 29-11-00/201).
(b) Push both of the captain's or both of the first officer's brake
pedals to the stops.
(c) Pull the parking brake lever.
(d) Release the brake pedals.
(e) Keep hydraulic system No. 4 pressurized for 30 seconds minimum.
NOTE: It is necessary to keep hydraulic system No. 4
pressurized for 30 seconds minimum for satisfactory
parking brake system pressure. You can keep hydraulic
system No. 4 pressurized more than 30 seconds to get
more pressure.
(f) Remove hydraulic system No. 4 pressure if it is not necessary
(AMM 29-11-00/201).
(2) Release the parking brake.
(a) Push both of the captain's or both of the first officer's brake
pedals to the stops.
NOTE: This will cause the parking brake lever to return
to the off position automatically.
(b) Release the brake pedals.
(3) To get parking brake indication and brake pressure indication during
towing, set the STBY switch on the P5 overhead panel to OFF, and set
the TOWING BAT PWR switch on the P461 aft overhead panel to the BAT
position.
(4) You can also get the parking brake indication and brake pressure
indication during towing if you do the steps that follow to use the
ground handling bus:
(a) Put the STBY switch on the P5 overhead panel to OFF
(b) Put the TOWING POWER BACKUP switch on the overhead panel, P461,
to the ENABLE position.
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