Landing Gear & Brakes

Table of Contents:-

Normal Procedures: (Refer to Chapter 4)

Alternate Operations:
  • Manual Nose Gear Extension
  • Manual Nose Gear Door Release
  • Gear Not Centred Light Illuminated
  • Landing Gear Lever Will Not Move to Up Position
  • Gear Door Open Light Remains Illuminated
  • Red Gear Light Remains Illuminated Following Gear Retraction
  • Anti-Skid GRD Mode Light Does Not Illuminate During Ground Test
  • Anti-Skid Light Illuminated
  • Anti-Skid Hydraulic Light Illuminated
  • Auto Brake Lights Illuminated
  • Brake Overheat Light Illuminated
  • Ground Safety Relay Light Illuminated Inflight
  • Brake Low Pressure Light Illuminated - See Chapter 2 Hydraulic System Leak or Loss


Controls and Indicators:
  • Landing Gear
  • Landing Gear Annunciator Module
  • Brake System
  • Anti-Skid
  • Brake Temperature
  • Auto Brake
  • Body Gear Steering and Landing Gear Alternate Extension
  • Nose Gear Manual Extension
  • Landing Gear Tilt Functions


Schematic:
  • Hydraulic Brake System

Supplementary Information:
  • Landing Gear
  • Brakes
  • Anti-Skid
  • Steering
  • Landing Gear Doors (Release Handles)
  • Brake Cooling
  • Brake Energy (Chart)

Cross Reference: Landing Gear Hydraulic Power - Refer to Hydraulic Power Chapter 16




Alternate Operations
Manual Nose Gear Extension
Manual Nose Gear Door Release
Gear Not Centred Light Illuminated
Landing Gear Lever Will Not Move to Up Position
Gear Door Open Light Remains Illuminated
Red Gear Light Remains Illuminated Following Gear Retraction
Anti-Skid GRD Mode Light Does Not Illuminate During Ground Test
Anti-Skid Light Illuminated
Anti-Skid Hydraulic Light Illuminated
Auto Brake Lights Illuminated
Brake Overheat Light Illuminated
Ground Safety Relay Light Illuminated Inflight
Brake Low Pressure Light Illuminated - See Chapter 2 Hydraulic System Leak or Loss


Controls and Indicators


Landing Gear:


Body Gear (Centre pair) will assist turning whilst taxiing when the "Body Gear Steering" (Capt Overhead Panel) is armed, ie switch guard up and switch armed. 


There are 18 wheels on the 747, so at maximum gross weight there is almost 21 tons on each tyre.











The centre pair of gear are powered by Hydraulic System No. 1, and will rotate up to 13 degress in the opposite direction to the nose gear.
This action is controlled by the tiller, not the rudder pedals. 
Note:  Take Off Warning Horn wil sound if BGS is not disarmed when No. 3 throttle is advanced for take off.



Gear Door Open Light:
Illuminates with any one indication of a door open.
Note: A door can be considered closed if either the primary or the alternate annunciator lights indicate door closed.

Landing Gear Lever Latch:
Locks landing gear lever out of UP detent when airplane is on the ground.  Automatically retracts when all primary or alternate body gear steering and tilt annunciator lights indicate gears are safe for retraction.
Note:  The lever latch can be released manually by moving the latch to the right to clear landing gear lever.

Landing Gear Lever:
OFF - Depressurises landing gear hydraulic system,

Gear Down Light (Green):
Illuminates when all landing gears are down and locked.
Note:  GEAR DOWN light will illuminate if all primary or alternate annunciator lights indicate gears down and locked.

Red Gear Light:
Illuminate (with a primary or alternate indication) for the following conditions:
- Landing gear(s) not down and locked and any thrust lever retarded to IDLE
- Landing gear(s) in transit or not in agreement with the landing gear lever.  Except light will not illuminate with gear and flaps up and landing gear lever in OFF position.
- Landing gear up with flaps in 25 or 30 position.


Warning Horn Cutout Switch:

Push to silence and reset horn.

With the landing gear not down and locked a steady horn will sound as follows:
- With the flaps in a maneuvring detent (1 through 20), any time a thrust lever is retarded to IDLE.  The horn can be silenced and reset with the warning horn cutout switch.
- With flaps 25 or 30 and thrust levers in any position, the warning horn can not be silenced.










Landing Gear Annunciator Module:

Door Annuciator Lights (Amber):
Will illuminate when checked with door open.

Gear Down Annunciator Lights (Green):
Will illuminate when checked with gear down and locked.
Note:
- Pilot's GEAR DOWN light will illuminate if all primary or all alternate gear down annunciator lights indicate gear down and locked.
- Pilot's red GEAR light will be illuminated with landing gear lever in DN position and any one primary or alternate gear down annunciator light indicates gear not down and locked.

Alternate Annunciator Switches:
Press and Hold - The response of selected alternate annunciator lights will be displayed.


Tilt Annunciator Lights (Amber):
Will illuminate when checked with airplane on ground (gear not tilted).
Note: Airplane inflight (indicated by the tilt annunciator lights extinguished):
- Releases landing gear lever latch
- Deactivates takeoff warning
- De-energizes the ground safety relay
- Activates anti-skid touchdown protection for normal brake system only
- Activates auto ground spoilers on landing


Brake System:


Hydraulic system 1

Hydraulic System 1 Select Light (Green):
I
lluminated when hydraulic system 1 is selected to pressurize brake system.

Normal Brake Source Switch:
Selects hydraulic power source for normal brake system.

Brake Low Pressure Light (Amber):
- Illuminates when selected brake system pressure is low.
- Extinguishes when hydraulic system 4 electric pump is pressurizing brake system.



Hydraulic system 4

Hydraulic System 4 Electric Pump Switch:

Primarily provided to power brakes during ground handling operations.











Hydraulic Brake Pressure Indicator:

Indicates normal brake pressure.
With no system pressure and parking brakes not set, indicates accumulator precharge pressure.




Brake Source Low Pressure Light (Amber):
On early airplanes:
- Illuminates when selected brake system pressure is low.
- Remains illuminated when hydraulic system electric pump is pressurizing brake system.
On later airplanes:
- Flashes when selected brake system pressure is low.
- Extinguishes when hydraulic system electric pump is pressurizing brake system.

Reserve Brake Valve Open Light (Green):
Illuminates when reserve brake valve is open.

Reserve Brake Switch:
Opens reserve brake valve pressurizing reserve brake system.
Note:  Parking brakes will not hold with hydraulic system No. 2 depressurised.




Parking Brake Lever



Parking Brake Lever:
To set brakes, move lever aft with brakes applied.
Apply brakes to release parking brake.

Parking Brake Light (Red):
Illuminates when parking brakes are set.





Nose Gear - Interphone Panel:
Brake Indicator Lights:
Amber indicates parking brake lever set.
Blue indicates brake pedals not depressed.
Red indicates brakes pressurized.


Anti Skid

Anti-Skid Switch:

OFF - ANTI-SKID light and all anti-skid annunciator lights will illuminate.

ON - Anti-skid system is operative when any one main gear is down and locked.







Anti Skid Light (Amber)
:
Illuminates to indicate electrical fault to the anti-skid system.
Note: ANTI-SKID light and anti-skid annunciator lights are deactivated when main landing gears are retracted.
Anti Skid Hydraulic Light (Amber):
- When illuminated, parking valve is not in the full open position.
- Anti-skid system may be inoperative when valve is not fully open.


Anti-skid Grd Mode Light (Green):
If light illuminates during test anti-skid operation is normal.

Anti-skid Grd Mode Test Switch:
FOR GROUND TEST ONLY - Hold in PRIM and ALT positions to check main landing gear on ground (not tilted) input to anti-skid system,



Anti-Skid Reserve Valve Annunciator Lights (Amber)
:
Illuminate to indicate an electrical fault in reserve anti-skid valve.

Anti-Skid Annunciator Lights (Amber):
Illuminates to indicate an anti-skid electrical fault for the indicated wheel.





Brake Temperature

Brake Temperature Indicators:
Indicate relative brake temperature.
Note:  An inoperative channel is indicated by a full scale deflection without an overheat light or a below scale indication.

F/E Brake Overheat Light (Amber):
- Illuminates when brake temperatures are high.
- If no wheels switches are depressed, overheat light monitors all brakes.
- If any wheels switch is depressed, overheat light only monitors wheels selected.

Brake Overheat Test Switch:
Introduces an overheat signal for all wheels.  Brakess overheat lights will illuminate.  Brake temperature indicators will give overheat indications when each wheels switch is depressed.

Wheels Switches:

- Each switch, when pressed and illuminated selects the four wheels to be monitored by the brake indicators.
- With all switches extinguished the brake overheat lights are active for all wheels.
- With no wheels switches depressed brake temperature indicators are inoperative.





Auto Brake

Auto Brake Take-off Arm Switch:
ARM - Arms the auto bra
ke system if the airplane is on the ground and the auto-brake LANDING arm switch is in OFF position.  Maximum braking will be applied in the event of a Rejected Take-Off (RTO) when:
- Wheelspeed is above 80 Knots
- Any symmetrical set of thrust levers are moved to reverse interlock position
- No brake pedal application
- Anti-Skid ON with no faults
- No auto-brake fault exists.


OFF:

- System is disarmed
- Switc
h will automatically more to OFF when airplane leaves the ground
- Switch must be moved to OFF to extinguish AUTO BRAKE light if system is disarmed by brake pedal application.

Auto-Brake Landing Arm Switch:
MIN - MED - MAX
- Auto-brake system is armed and deceleration level selected when switch is electronically held in MIN, MED or MAX position.
- Brakes will be applied when airplane is on the ground and wheel spin-up has occurred.
- Switch will automatically move to DISARM position and AUTO BRAKE light will flash if:
- Brake pedal(s) are depressed
- Airplane on the ground and No. 1 or 3 thrust levers in take-off range
- Anti-skid system is not ON or a fault exists
- Auto-brake system fault or loss of electrical power
- Landing gear tilt functions not in agreement.
DISARM - Brake pressure will release (if applied) and AUTO BRAKE light will flash when switch is in DISARM position.
OFF - Positioning switch to OFF will extinguish AUTO BRAKE light.



Body Gear Steering

Body Gear Steering Switch:

DISARM position deactivates body gear steering for takeoff and landing.
ARM position activates body gear steering for taxi and towing operations.





Body Gear Not Centred Light (Amber):
Illuminates for either a PRIM or ALT body gear unlocked indication.
Note:  A warning horn will sound on advancing No 3 thrust lever for takeoff and landing gear lever latch will not release with PRIM or ALT indication that body gear is not centred.

Body Gear Steering Pressure Light (Amber):
Illuminates when body gear steering is powered and nose gear steering is being utilized.
Body Gear Steering Unlocked Lights (Amber):
Illuminates for an unlocked indication for the selected PRIM or ALT systems.
Body Gear Steering Annunciator Switch:
Monitors steering locked indications for selected PRIM or ALT systems.


Landing Gear Alternate Extension


Alternate Gear Extend Switches:

EXT - Hold to initiate the landing gear extension cycle.  Door annunciator light will illuminate indicating extension cycle has started.

ARM - Leave in ARM position to continue alternate extend cycle.






Nose Gear Manual Extension
- E & E Compartment - Instructions are placarded

Left Side of Nose Wheel Well Cover

Wrench:
To lock after nose gear is extended insert wrench through crank flange and matching hole above lower drive shaft socket.

Crank:
Insert in lower drive shaft socket to manually lower nose gear.

Lock Shaft Adapter:
Note:  One end of the indicator is red and lock shaft indicator line is on lug.


Landing Gear Tilt Functions

- Flight mode
- Landing gear tilt
- Ground mode
- Flight mode (Oleo extended)
- Ground mode (Oleo compressed).



Schematic
Hydraulic Brake System

Supplementary Information

Landing Gear:

Normal power for landing gear extension and retraction is supplied by two independant hydraulic sources: Hydraulic system No. 1 for the nose and body gear and system No. 4 for the wing gear.  The alternate extension system uses electric motors to unlock the doors and landing gear.  Landing gear weight and air loading extend the gear to the locked position.  Manual extension is also provided for the nose gear.  Landing gear doors require hydraulic power to close after being opened.  During initial retraction, automatic braking is applied to the main gear wheels.

The main landing gear trucks must be in a tilted and centred position before retracting the landing gear.  A lever latch prevents the landing gear lever from being moved to the UP position until all primary or all alternate sensors indicate gears are safe for retraction.  The lever latch can be manually moved allowing the landing gear to be retracted.

The landing gear is designed to permit emergency landings with a combination of any one main gear on each side and the nose gear down and locked.

Landing Gear Position Sensors:
A primary and an alternate system of sensors are used for landing gear position indications and warnings.  The system has sensors to determine the following:
- gear down and locked
- gear up and locked
- gear tilted
- gear doors closed

Annunciator lights are provided on the flight engineer's landing gear annunciator module to display the indications from either the primary or alternate system.  Annunciator lights are not provided for the gear up and locked sensors.

Ground Safety Relay:
The ground safety relay determines the mode of operation of various aircraft systems.  Tilt sensors on the wing and body gear provide input to the ground safety relay.  This relay illuminates the GRD SAF RELAY ON light for a ground mode.  The
GRD SAF RELAY ON light also illuminates when the nose squat switches disagree.  However, the nose squat switches do not affect the ground safety relay functions.


Brakes:

All the main landing gear wheels have hydraulic braking.  The normal brake system is powered by the No. 4 hydraulic system, with system No. 1 as the alternate source.  When utilizing system No. 1 as an alternate source, common tubing is utilized downstream of the normal brake source select valve.  The brake pressure indicator reflects the normal brake system pressure at the pneumatic end of the accumulator when using either system No. 4 or No. 1.  With loss of system
hydraulic pressure, the brake pressure should hold unless the brake pedals are depressed or a leak has occurred in the normal brake system.

The accumulator is primariliy for holding parking brakes.  It will not stop the airplane if normal brake system pressure is lost.
A reserve brake system, powered by the No. 2
hydraulic system is also provided.  Braking with either the normal or reserve brake system is modulated by the anti-skid system.  The reserve brake system does not have touchdown protection.  When using the reserve brake system, parking brakes will not hold unless hydraulic system No. 2 is kept pressurized.

The auto braking system will automatically apply maximum brakes for a rejected takeoff when reverse thrust is initiated and on landing will apply brakes at a selected level after wheel spin-up.

Protective features are installed that will automatically disarm the system when a fault exists or when auto brakes are not operating.
Auto brake system will not operate when using the reserve brake system.  Auto brakes should not be armed when ANTI SKID HYD light is illuminated.


Anti-Skid:

The anit-skid system modulates the brake pressure to prevent tyre damage and skidding of the wheels.  With the anti-skid switch in the ON position, the system is operative when one or more main landing gear are down and locked.  The system has annunicator lights to indicate system malfunctions.  The anti-skid system is inoperative and anti-skid
hydraulic light is illuminated when the parking brake valve is not fully open.

Locked wheel protection is provided for each wheel to prevent a wheel locking when landing on wet or icy runways.

The system provides protection against inadvertent brake application at touchdown (touchdown protection).  This function is controlled by an input from the landing gear tilt sensors which electrically prevents braking until one gear on each side of the airplane is on the ground.


Steering:

The No. 1 hydraulic system powers nose and body gear steering.
Both pilot's tillers and rudder pedals control nose wheel steering.  Rudder pedals provide up to 7 degrees of steering and can be overridden by tillers.  Body gear steering is controlled by nose wheel position.  Body gear steering operates automatically during medium to sharp turns.  All steering is deactivated in flight.  A switch deactivates body gear steering for takeoffs and landings.  If BGS is deactivated in a turn the body gear is centred.

With
hydraulic system No. 1 depressurised, use of the tiller in the direction of turn improves turning capability.  However, application of high forces on the nose wheel tiller may result in misalignment of the nose gear and tiller.


Landing Gear Doors (Release Handles):
The
hydraulically actuated doors are powered by the hydraulic systems used to operate the respective gear; hydraulic system No. 1 for nose and body gear; hydraulic system No. 4 for wing gear.
Two ground release handles, one in each body gear well, release both wing and body gear doors on the respective side of the airplane.  One ground door release handle is in the nose wheel well.  Operating instructions are located at each handle.
Landing gear door release handles must be in the DOOR OPEN position and locked while doors are open.  Before pressurizing
hydraulic systems 1 or 4, the position of the doors and release handles should be verified.


Brake Cooling:

To prevent the possibility of tyres deflating, precautions are necessary when using excessive braking.
High energy stops, prolonged taxiing or short flight segments without adequate in flight cooling time can result in brake overheat.
The brake temperature indicators may be used to determine approximate brake temperature levels ONLY after temperatures have peaked and commence to decrease.
Temperatures may rise for fifteen minutes or more before stabilizing.  Refer to Chapter 4, Adverse Weather, for additional information on brake operation and cooling. 
A BRAKE EFFICIENCY CHART in the QRH and a BRAKE COOLING SCHEDULE in Chapter 23.10 provide data to determine brake energy levels and cooling times.  Consult this schedule for recommended brake cooling time.
Caution: In flight, with gear down the brake temperature indicator may indicate as much as 2 units below the actual, due to location of the pickup.

The brake temperature indicator will provide relative brake temperature levels, with parking brakes set or release, ONLY after brake temperatures have peaked and begin decreasing.  Temperatures may rise for fifteen minutes or more after braking before stabilizing.

On the ground:

With temperatures in the RED band and/or brake overheat light illuminated:
Do Not Takeoff - Minimise braking if practical.  Fuse plugs may melt and deflate tyres.

With temperatures Stabilized in the Amber Band:
A recent high gross weight landing, a previously rejected takeoff, high gross weights, high ambient temperatures and tailwinds are factors to be considered before takeoff.  A subsequent rejected takeoff is likely to result in melted fuse plugs and possible brake fires.
Consult the BRAKE COOLING SCHEDULE in Chapter 23.10 to determine if brake cooling is recommend before takeoff.

Inflight:

With a brake temperature in the RED band and/or if the brake OVERHEAT light illuminates, extend landing gear to cool brakes.
Observe gear placard speeds.
When brake temperatures have decreased into the GREEN band, retract the gear, continue flight and be prepared for possible flat tyres on landing.
Caution: Inflight, with gear down, the brake temperature indicator may indicate as much as 2 inits below actual due to location of the temperature pick up.

After a short flight, or a series of short flights, the brake temperature indicator may still indicate in the AMBER band.
If the subsequent landing will require a maximum braking effort, extend the gear early to cool the brakes to the GREEN band. 
Consult the Brake Cooling Schedule in Chapter 23.10 for recommended cooling times.

Brake Energy (Chart):

0-3 Units - Green Band - No Special Procedure
3-7 Units - Amber Band - Observe Cooling Times
7-8 Units - Red Band - Caution Plugs May Melt
8-10 Units - Red Band - Danger Plugs Melt

0-45 Millions of Foot Pounds - Brake Energy Per Brake


Limitations:

Extend: 270 knots / M 0.82, Retract: 250 knots / M 0.82, Extended: 320 knots / M 0.82.  Alt Ext: 230kts/.82M. 

Ground speed max: 204kts.

                      
Degrees of NGS max - w/ rudders 7 degrees    w/ tiller:  70 degrees.

NLG: 180-185psi.

MLG: 195-200psi.

Size all gear: 49x19-20 34 PR.




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