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Difference between revisions of "Tyres"

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|control_caption  = Eurocontrol
 
|control_caption  = Eurocontrol
 
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==Definition==
 
 
A brake is a device for slowing or stopping the motion of a machine or vehicle, or restraining it from starting to move again.
 
  
 
==Description==
 
==Description==
 
   
 
   
Aircraft brakes are located on the main wheels and are usually applied by either a hand control or by foot pedals (toe or heel), although on modern aircraft, automated braking systems are also becoming prevalent. Wheel brakes operate independently in order to allow for differential braking, which can supplement nosewheel/tailwheel steering during ground operations. The kinetic energy lost by slowing an aircraft down is usually translated into heat by friction. Anti-Skid or Anti-Lock Braking Systems (ABS) are designed to minimise the amount skidding that occurs when a wheel is stopped from rotating ie locked, thus minimising the potential for tyre damage.
+
Aircraft tyres are designed to withstand extremely heavy loads for short durations, with the number of tyres required increasing with the weight of the plane in order to better distribute the weight.
 +
 
 +
Aircraft tyre tread patterns are designed to facilitate stability in high crosswind conditions, to channel water away to prevent aquaplaning, and for braking effect. Some types of nose wheel tyres include one (or two) chine moulded into the rubber on the shoulder buttresses that deflects water away during aircraft movement on a wet runway. Aircraft tyres also include heat fuses (sometimes called fusible plugs) which are designed to melt at a certain temperature in order to reduce the risk of an explosive deflation due to overheating.
  
 
==Effects==
 
==Effects==
  
*Overheated brakes
+
There are 2 primary hazards associated with tyres:
**Loss of braking performance
 
**Fire
 
**Tyre deflation
 
  
*Brake failure
+
*'''Deflation;''' the tyre deflates in a controlled manner with minimal direct consequence to other systems.
**Runway excursions
 
**Uncommanded aircraft ground movements
 
  
==Defences==
+
*'''Explosive break-up;''' the tyre (and sometimes the wheel holding the tyre) deflates or breaks-up in an uncontrolled manner with a significant probability of secondary damage to other unrelated systems.
 
Minimise brake applications by adjusting power settings when possible, including the use of reverse thrust.
 
  
If heavy braking has to be undertaken, ensure an adequate cooling period follows, otherwise subsequent braking performance may be degraded, along with the potential for tyre overheating to occur.
+
These hazards are associated with 4 distinct periods of aircraft operation:
  
Leave the gear down for protracted periods if overheating is suspected.
+
*Ground operations eg taxying
Know how the brake system operates; each system will have specific instructions associated with it.
+
*Take-off (up to gear retraction)
 +
*Post take-off (gear stowed)
 +
*Landing (to the end of the roll-out)
  
Stay aware for uncommanded ground movements; don’t become too engrossed inside the cockpit when on the ground.
+
The various combinations of hazard and flight period can have markedly different influences, but all can affect operations to some degree.
  
==Typical Scenarios==
+
==Defences==
 +
 +
*'''Aircraft Maintenance & Ground Maoeuvre:''' operating with the correct tyre pressures and maximising turn radii during ground manoeuvres can mitigate against a number of contributing factors associated with overheating and wear issues which can lead to tyre failure.
  
The following are extracts from real-life incidents:
+
*'''Procedures:''' managing taxy patterns, reduced taxy speeds and allowing sufficient cooling time when necessary can also obviate the issues associated with overheating. In-cockpit procedures for landing can also influence the occurrence of damage to the tyres.
  
*After landing the aircraft did not decelerating normally and the FO announced ‘Manual Braking’. The commander pressed the brakes without effect. The crew then... The commander braked to bring the aircraft to a halt about 40 metres from the end of the runway, bursting three mainwheel tyres. Analysis showed that it took ten to thirteen seconds for the commander to recognise the lack of pedal braking and there was no overt warning from the ...
+
*'''Inspections:''' aircraft tyre inspections can identify a worn or damaged tyre that can subsequently be changed before it may explosively deflate or breaks-up, whilst airfield FOD inspections can reduce the possibility of undetected damage occurring after the inspection.
  
*Shortly after commencing the taxi for takeoff, a hydraulic union in the braking system fractured, causing fluid to leak from the Yellow hydraulic system. The departure was cancelled and the aircraft returned to the terminal. After stopping on the allocated stand, the parking brake was selected on, but the brakes failed to apply, as the parking brake is operated by the Yellow hydraulic system. The aircraft then began to move forward under idle engine power... The aircraft collided with the airbridge, damaging the left engine inlet cowl, before coming to a stop.
+
==Typical Scenarios==
 
+
*Having carried out the normal pre-flight checks the pilot released the parking brake by fully depressing the brake pedals prior to taxi. The aircraft was taxied to the threshold of Runway 05, a distance of nearly 2 nm, which took approximately 10 minutes. During this time the engine was running at 1000-1200 rpm and the brakes were rarely operated. Just before arriving at the holding point the pilot noticed "dust - like" smoke coming from the area of the left wheel, the volume of which rapidly increased as the aircraft was brought to a halt.
+
Taxying: Long taxy patterns at heavy weights with tight turns will generate a lot of heat in the tyres, even if the brakes are used sparingly. This could cause the heat fuses to melt, resulting in a controlled deflation of the tyre. Dependent upon a number of factors, including the remaining number of tyres on the aircraft, there may be restrictions on further aircraft movement prior to the wheel being changed.
 +
Take-off: High speed aborts generate a great deal of heat in both the brakes and the tyres and restrictions may need to be placed on the degree of ground movement that can be undertaken after an abort. The potential consequences of a high speed abort are, therefore, the melting of the heat fuses and the consequential impact as above.
 +
Take-off: Explosive deflation/break-up due to eg FOD can have catastrophic consequences. There is a great deal of potential energy stored in the tyre/wheel assemblies and multiple, unrelated system damage should be anticipated. An immediate landing will be the priority.
 +
Post take-off: Rapid retraction of the undercarriage following a long, high speed, heavy weight taxy with immediate take-off, or multiple touch-and-goes during crew training, can lead to the tyres overheating in the wheel well. The heat fuses should prevent an explosive deflation, but it is not guaranteed. The main problem with this event is that the crew are potentially unaware that they have an issue with the undercarriage until secondary effects start to occur during the landing run.
  
*After starting the engine, the aircraft began to move forward. Despite repeatedly operating the toe brakes, the aircraft swung round, resulting in its left wing contacting the left wing of an adjacent aircraft, and its right wing striking the wall of a shed.  
+
Landing: A number of issues can arise from landing with a deflated tyre:
 +
• Handling issues may arise during the landing roll-out phase, and in severe cases may cause the aircraft to depart the prepared surface.
 +
• Landing with a deflated tyre will put additional strain on the remaining tyres, with an increased potential for one or more to subsequently suffer an explosive deflation due to overstress. The implication for secondary damage to the aircraft is high and the potential for rapid aircraft arrest and evacuation is enhanced.
  
 
==Contributory Factors==
 
==Contributory Factors==
 
   
 
   
*Over-reliance on automated systems which subsequently fail.
+
*Foreign Object Damage (FOD) around the operating areas
*There is evidence that the fitting of ABS brakes to cars has had an undesirable effect in that drivers have started to drive far more aggressively, believing that they are now much safer. It could be considered not unreasonable to assume that the same psyche may pervade the cockpit. 
+
*Minimal time between push-back/start-up and take-off slot time
*Misunderstanding of the abilities of a braking system; ABS can actually INCREASE the braking distance under some circumstances eg ice, snow, gravel and “soft” surfaces.
+
*Lighting conditions for inspections
*ABS does not prevent aquaplaning.
 
*Spats and leg fairings (which are particularly prevalent on GA aircraft) can lead to poor brake cooling and act as traps for material which can act as a source of ignition for fires.
 
 
 
  
 
==Solutions==
 
==Solutions==
  
If it is known that the brakes (and tyres) may be hot then the following precautions may be prudent in order to allow the components time to cool:
+
Plan for slower taxy speeds with gentler turning radii.
 +
If it is known that the tyres (and brakes) may be hot then the following precautions may be prudent in order to allow the components time to cool:
 
*Leave the gear down for a protracted period after take-off.
 
*Leave the gear down for a protracted period after take-off.
 
*If at all possible, avoid committing to a landing very soon after take-off.
 
*If at all possible, avoid committing to a landing very soon after take-off.
 
*Follow the Flight Manual guidelines on cooling periods for example after an emergency stop at whatever speed.
 
*Follow the Flight Manual guidelines on cooling periods for example after an emergency stop at whatever speed.
  
Consider whether Hot Brake incidents should be attended by fire crews.
+
Ground controllers should consider where they would place an aircraft that requires a prolonged cooling period on the ground so as to minimise disruption to other traffic.
 +
Ensure adequate FOD control measures are in place and adhered to.
  
Ground controllers should consider where they would place an aircraft that requires a prolonged cooling period on the ground so as to minimise disruption to other traffic.
+
==Further Reading==
  
==Related Articles==
+
*Concorde Accident Report
*[[Aircraft Braking System]]  
+
*[[Tyres – Inflation Pressures]]
*[[Brake Fire]]
+
*[[Tyres – Speed Limits]]
 +
*[[Tyres – Tread Wear and Tyre Damage]]
 +
*[[Tyres – Overheating]]
 +
*[[Brakes]]  
 
*[[Aquaplaning]]
 
*[[Aquaplaning]]
 
==Further Reading==
 
 
*[Automatic Braking System Failure
 
 
  
  
 
[[Category:Flight Technical]]
 
[[Category:Flight Technical]]
 
[[Category:Enhancing Safety]]
 
[[Category:Enhancing Safety]]

Revision as of 14:10, 30 June 2008

Article Information
Category: Flight Technical Flight Technical
Content source: Skybrary skybrary
Content control: Eurocontrol Eurocontrol

Description

Aircraft tyres are designed to withstand extremely heavy loads for short durations, with the number of tyres required increasing with the weight of the plane in order to better distribute the weight.

Aircraft tyre tread patterns are designed to facilitate stability in high crosswind conditions, to channel water away to prevent aquaplaning, and for braking effect. Some types of nose wheel tyres include one (or two) chine moulded into the rubber on the shoulder buttresses that deflects water away during aircraft movement on a wet runway. Aircraft tyres also include heat fuses (sometimes called fusible plugs) which are designed to melt at a certain temperature in order to reduce the risk of an explosive deflation due to overheating.

Effects

There are 2 primary hazards associated with tyres:

  • Deflation; the tyre deflates in a controlled manner with minimal direct consequence to other systems.
  • Explosive break-up; the tyre (and sometimes the wheel holding the tyre) deflates or breaks-up in an uncontrolled manner with a significant probability of secondary damage to other unrelated systems.

These hazards are associated with 4 distinct periods of aircraft operation:

  • Ground operations eg taxying
  • Take-off (up to gear retraction)
  • Post take-off (gear stowed)
  • Landing (to the end of the roll-out)

The various combinations of hazard and flight period can have markedly different influences, but all can affect operations to some degree.

Defences

  • Aircraft Maintenance & Ground Maoeuvre: operating with the correct tyre pressures and maximising turn radii during ground manoeuvres can mitigate against a number of contributing factors associated with overheating and wear issues which can lead to tyre failure.
  • Procedures: managing taxy patterns, reduced taxy speeds and allowing sufficient cooling time when necessary can also obviate the issues associated with overheating. In-cockpit procedures for landing can also influence the occurrence of damage to the tyres.
  • Inspections: aircraft tyre inspections can identify a worn or damaged tyre that can subsequently be changed before it may explosively deflate or breaks-up, whilst airfield FOD inspections can reduce the possibility of undetected damage occurring after the inspection.

Typical Scenarios

Taxying: Long taxy patterns at heavy weights with tight turns will generate a lot of heat in the tyres, even if the brakes are used sparingly. This could cause the heat fuses to melt, resulting in a controlled deflation of the tyre. Dependent upon a number of factors, including the remaining number of tyres on the aircraft, there may be restrictions on further aircraft movement prior to the wheel being changed. Take-off: High speed aborts generate a great deal of heat in both the brakes and the tyres and restrictions may need to be placed on the degree of ground movement that can be undertaken after an abort. The potential consequences of a high speed abort are, therefore, the melting of the heat fuses and the consequential impact as above. Take-off: Explosive deflation/break-up due to eg FOD can have catastrophic consequences. There is a great deal of potential energy stored in the tyre/wheel assemblies and multiple, unrelated system damage should be anticipated. An immediate landing will be the priority. Post take-off: Rapid retraction of the undercarriage following a long, high speed, heavy weight taxy with immediate take-off, or multiple touch-and-goes during crew training, can lead to the tyres overheating in the wheel well. The heat fuses should prevent an explosive deflation, but it is not guaranteed. The main problem with this event is that the crew are potentially unaware that they have an issue with the undercarriage until secondary effects start to occur during the landing run.

Landing: A number of issues can arise from landing with a deflated tyre: • Handling issues may arise during the landing roll-out phase, and in severe cases may cause the aircraft to depart the prepared surface. • Landing with a deflated tyre will put additional strain on the remaining tyres, with an increased potential for one or more to subsequently suffer an explosive deflation due to overstress. The implication for secondary damage to the aircraft is high and the potential for rapid aircraft arrest and evacuation is enhanced.

Contributory Factors

  • Foreign Object Damage (FOD) around the operating areas
  • Minimal time between push-back/start-up and take-off slot time
  • Lighting conditions for inspections

Solutions

Plan for slower taxy speeds with gentler turning radii. If it is known that the tyres (and brakes) may be hot then the following precautions may be prudent in order to allow the components time to cool:

  • Leave the gear down for a protracted period after take-off.
  • If at all possible, avoid committing to a landing very soon after take-off.
  • Follow the Flight Manual guidelines on cooling periods for example after an emergency stop at whatever speed.

Ground controllers should consider where they would place an aircraft that requires a prolonged cooling period on the ground so as to minimise disruption to other traffic. Ensure adequate FOD control measures are in place and adhered to.

Further Reading