Chapter 7 - Wheels, Brakes, Tyres

Question 1

What are ‘ Creep Marks’?

Answer 1

White marks which are painted onto the tyres to show if the wheel is rotation within the hub.
If it was to move around too far, then the valve could blow the tyre.
1” width for 24” Tyres.
1.5” width for more than 24” Tyres.

Question 2

What is ‘Vtyre’?

Answer 2

The tyre speed rating.
The maximum speed that the tyre can be used at.
- Rated in MILES PER HOUR (MPH)

Question 3

What should be looked for when inspecting a tyre?

Answer 3

• Cuts
• Bulges
• Flat Spots
• Foreign Object Damage
• Contamination (Fluid spillage onto the tyre).
• Creep
• Wear
• Pressure

Question 4

What are the correct tyre pressures? And why is it important?

Answer 4

Low = up too 200psi
High = 200-315psi

Over Inflation leads to excess wear and possible blow out.
Under Inflation can lead to tyre creep, excess heat, wear and failure.

IF ONE TYRE IS PUNCTURED THEN THE WHOLE BOGIE IS REPLACED.

Question 5

What is a Fusible Plug?

Answer 5

The plug/valve that goes into the tyre will melt at high temperature.
This prevents the engine exploding at high heat.

Question 6

What brakes are used on a Light Aircraft?

Answer 6

Simple Single Discs - Passive System.

Question 7

What brakes are used on a Large Transport Aircraft?

Answer 7

Multiple Disc Park System.
Typically using Hydraulic Power.
Active System.

787 uses electrical power.

Question 8

Brakes work by converting ______ Energy into ______ Energy through Friction.

Answer 8

Brakes work by converting KINETIC Energy into HEAT Energy through Friction.

Question 9

The brakes should be checked when…?

Answer 9

The brakes should be checked when the brakes are APPLIED.

Question 10

How are the breaks and tyres checked?

Answer 10

Rule or special gauge.

Some aircraft are equipped with Break Wear Indicator Pins.

Question 11

Mechanical Process of a brake activating?

Answer 11

Brake pressure applied to the back of the piston.
Disk loves laterally until it makes contact with the friction pad.
A return spring pulls the piston off when the pressure is released.

Question 12

What is ‘Brake Fade’?

Answer 12

On steel brakes, when the excessive heat diminishes the braking efficiency.
- If the brakes are underperforming then try releasing the brakes temporarily, when reapplying them.

Question 13

What is the purpose of a ‘Automatic Brake Adjustor’?

Answer 13

Ensures correct clearance between the rotating assemblies when the brakes are in the off position.

Question 14

What is the purpose of a ‘Brake Wear Indicator Pin’?

Answer 14

As the brake pads wear down the pin starts to retract in the housing.
The pads must be replaced when the end of the pin is flush with the housing.

Question 15

Carbon brakes.
Advantages
Disadvantages

Answer 15

Lighter, Less prone to brake fade, 30-175% improvement.

They are much more expensive.

Question 16

What is ‘Minimum Brake Hold-Over’?

Answer 16

The minimum amount of time needed for the brakes to cool down before takeoff is permitted.

Heat is usually shown on the ECAM.

Question 17

How does ‘Anti-skid’ work?

Answer 17

Prevents the wheels from skidding.
If skidding is detected then the brake will momentarily be released and applied.
This can be done several times a second.

Question 18

What is ‘Touch Down Protection’?

Answer 18

Prevents the brakes from being pre-applies before touchdown.

Even if the pilots applies the brake it will not work.

Question 19

What is ‘Bounce Protection’?

Answer 19

If the aircraft bounces, it releases the wheel brakes, until it touches down again.
This allows the wheels to spin back up, to reduce shock.

Question 20

Electronic Anti-Skid System Theory of Operation? (Long and painful)

Answer 20

• Tacho-generator driven by a wheel generates electrical output that varies with the wheel speed.
• The anti-skid controller cross-references signals from all wheels.
• Controller determines aircraft speed & thus speed of an un-braked wheel.
• Controller determines the Slip ratio between the theoretical un-braked (idler) wheel & braked wheel.
• Controller dumps brake pressure when the measured slip ratio reaches a pre-determined ideal value.
• After dumping brake pressure the controller reapplies a lower pressure and then rises steadily back towards maximum braking force.
  Changeover circuits couple valve for all brake units so that loss of speed signal from one unit does’nt affect the other.

Question 21

Where is Hydroplane Prevention located? (Which wheel?)

Answer 21

Given to the rear wheel on the bogie trolley, as this is the first to touch down.

Question 22

Difference between Hydroplaning and Aquaplaning?

Answer 22

Hydroplaning is the onset when the water is building.

Aquaplaning is full on ‘no friction’.

Question 23

What is the purpose of ‘Autobraking’?

Answer 23

Brings the aircraft to a stop without input from the pilot.

The amount of brake pressure is determined by a setting on the flight deck.

Question 24

Parameters for ‘Auto-brake’ to work?

Answer 24

• Auto brake must be ON & Serviceable.
• Anti-skid system must be ON and Serviceable.
• Power levers must be set below a certain value.
• Hydraulic system must be functional.
• Brake pedals must be depressed.

Question 25

Auto brake will be automatically deactivated if?

Answer 25

• Brakes are manually applied.

- Power is set to TO/GA

Question 26

Auto brake ‘RTO’ will activate when what parameters are met?

Answer 26

• Speed is greater than 90knots.
• Thrust Levers are idle.

BRAKING WILL DISARM THE SYSTEM!

Question 27

If Anti-Skid has a failure what may be the consequences? How will the aircraft show you the fault?

Answer 27

Landing distance may double.

Amber Warning Caution will illuminate if a fault is detected.

Question 28

What is the purpose of:
Brake Snubber?
Flight Brake?

Answer 28

Stop the wheel from rotating as it is stowed.

Question 29

What happens to the brakes in the case of Hydraulic Failure?

Answer 29

• 2 Hydraulic systems will produce the braking force.
• If that fails a brake accumulator can be used for 6 applications of brake.
• No Anti-skid.
• No differential braking.
• Directional control problems may occur.

Question 30

Parking Brake facts?

Answer 30

Parking brake overrides all other braking systems.
IT MUST NOT BE USED WHILE AIRBOURNE.
Cannot be set until the brakes have cooled down (Short taxi=bad)