the ability for low-cost airlines to maintain satisfactory safety standards
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the ability for low-cost airlines to maintain satisfactory safety standards
An interesting article from:
http://www.etravelblackboard.com/ind...nav=2&id=69284
Budget carriers: low cost, high risk?
Tuesday, 18 September 2007
The crash of Thai budget carrier One-Two-Go is the latest in a line of air disasters involving low cost carriers. According to an article by Asia Sentinel, the crash has raised concerns regarding the ability for low-cost airlines to maintain satisfactory safety standards.
In 2006, the growth of low-cost flights operating to and from Asia increased 666 percent from 2005, according to a report by Business Week. This surge in low cost carriers has undoubtedly fuelled competition on routes traditionally monopolised by flag carriers and lowered airfares for everyday consumers.
However, in many markets across Asia, fares have dropped so low that many are questioning the standard of safety inspection and maintenance procedures. For instance, this month, low-cost carriers AirAsia X and Jetstar are offering promotional flights from Kuala Lumpur to Melbourne for just RM10 (US$2.89).
The increase in flight volume, coupled with low cost pressures has placed increased strain on the entire aviation industry in Asia. The Chinese and Indian aviation sectors alone require some 4,000 new pilots each year. According to Asia Sentinel, out of the 1.2 million pilots in Asia, only 14 percent have qualified for the Professional Airline Pilots License.
No doubt, this has played a contributing factor to the many air safety disasters that have occurred in Asia since 2004. For instance, when Indonesia’s Adam Air reported a missing Boeing 737-400 on New Year’s Day, pieces were later found 300 kilometres offshore. In February, another Adam Air 737 cracked in half when it hit the ground at Surabaya airport. An audit of Indonesia’s airlines revealed that out of the 51 low cost carriers operating in the country, eleven did not fulfil civil aviation requirements and seven others were considered ‘least safe’.
In a study titled “Perspectives on the Development of Low-Cost Airlines in Southeast Asia” by Juliana Kim and Tom Baum at the University of Strathclyde in Glasgow, it is suggested that low-cost carriers are able to offer low prices because they cut expenses to the bone. For instance, AirAsia has an aircraft turn around time of 22 minutes at Kuala Lumpur International Airport and keeps planes in the air 10 hours a day. Pilots are also taught to burn 770 US gallons of fuel per hour, compared with the 1,100 gallons burnt per hour by Malaysia Airlines. As a result, AirAsia has the lowest costs per average seat per kilometre in the world.
Pilots will also attempt to land under considerably lower tolerances in order to cut costs – much to the detriment of customer safety. According to eyewitness reports, the One-Two-Go crash at Phuket occurred in rain and wind so heavy that trees were bending over. The aircraft only received permission to abort the landing at the last minute, when it skidded off the runway and burst into flames.
While a lower bottom line ensures lower prices for customers, does this discount come at a higher cost later on?
http://www.etravelblackboard.com/ind...nav=2&id=69284
Budget carriers: low cost, high risk?
Tuesday, 18 September 2007
The crash of Thai budget carrier One-Two-Go is the latest in a line of air disasters involving low cost carriers. According to an article by Asia Sentinel, the crash has raised concerns regarding the ability for low-cost airlines to maintain satisfactory safety standards.
In 2006, the growth of low-cost flights operating to and from Asia increased 666 percent from 2005, according to a report by Business Week. This surge in low cost carriers has undoubtedly fuelled competition on routes traditionally monopolised by flag carriers and lowered airfares for everyday consumers.
However, in many markets across Asia, fares have dropped so low that many are questioning the standard of safety inspection and maintenance procedures. For instance, this month, low-cost carriers AirAsia X and Jetstar are offering promotional flights from Kuala Lumpur to Melbourne for just RM10 (US$2.89).
The increase in flight volume, coupled with low cost pressures has placed increased strain on the entire aviation industry in Asia. The Chinese and Indian aviation sectors alone require some 4,000 new pilots each year. According to Asia Sentinel, out of the 1.2 million pilots in Asia, only 14 percent have qualified for the Professional Airline Pilots License.
No doubt, this has played a contributing factor to the many air safety disasters that have occurred in Asia since 2004. For instance, when Indonesia’s Adam Air reported a missing Boeing 737-400 on New Year’s Day, pieces were later found 300 kilometres offshore. In February, another Adam Air 737 cracked in half when it hit the ground at Surabaya airport. An audit of Indonesia’s airlines revealed that out of the 51 low cost carriers operating in the country, eleven did not fulfil civil aviation requirements and seven others were considered ‘least safe’.
In a study titled “Perspectives on the Development of Low-Cost Airlines in Southeast Asia” by Juliana Kim and Tom Baum at the University of Strathclyde in Glasgow, it is suggested that low-cost carriers are able to offer low prices because they cut expenses to the bone. For instance, AirAsia has an aircraft turn around time of 22 minutes at Kuala Lumpur International Airport and keeps planes in the air 10 hours a day. Pilots are also taught to burn 770 US gallons of fuel per hour, compared with the 1,100 gallons burnt per hour by Malaysia Airlines. As a result, AirAsia has the lowest costs per average seat per kilometre in the world.
Pilots will also attempt to land under considerably lower tolerances in order to cut costs – much to the detriment of customer safety. According to eyewitness reports, the One-Two-Go crash at Phuket occurred in rain and wind so heavy that trees were bending over. The aircraft only received permission to abort the landing at the last minute, when it skidded off the runway and burst into flames.
While a lower bottom line ensures lower prices for customers, does this discount come at a higher cost later on?
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The same aircraft, burning roughly the same fuel, carrying a similar number of passengers....
Something has to give and it is usually sadly a disaster that starts the circle of analysis.
Something has to give and it is usually sadly a disaster that starts the circle of analysis.
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I have great trouble with the efficacy of this article.
In a world where jet engine design is a mature technology and a 1% reduction in fuel burn is a landmark improvement, burning 30% less fuel on the same aircraft is simply not possible. Unless of course Malaysian airlines pilots fly everywhere at FL250 and mach 0.9.
The other comment,
is simply yet another confirmation of the overwhelming ignorance of the Press, and in turn the public, on what we actually do for a living.
Pilots are also taught to burn 770 US gallons of fuel per hour, compared with the 1,100 gallons burnt per hour by Malaysia Airlines.
The other comment,
The aircraft only received permission to abort the landing at the last minute
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For instance, AirAsia has an aircraft turn around time of 22 minutes at Kuala Lumpur International Airport and keeps planes in the air 10 hours a day. Pilots are also taught to burn 770 US gallons of fuel per hour, compared with the 1,100 gallons burnt per hour by Malaysia Airlines.
If you asked me, am glad my piloting skills aren't as bad as the Journo's ......
I'm afraid that while the article is awful, the question still has to asked.
Problems with maintenance, training and experience levels do not simply appear overnight, it takes many many years of cost cutting and cheese paring to increase the probability of an unsafe situation developing into an accident.
Then of course you have Aircraft manufacturers designing in new technology that in theory increases safety levels.
However, there is a sad human phenomenon called "risk shifting", which is when the introduction of a safer technology is offset by increasing the level of risk in other areas, so that the total level of risk remains the same.
Best example I am aware of is ABS in cars, has it reduced the frequency of nose to tail crashes? Apparently not, because drivers compensate for better brakes by driving closer together.
Compound this situation by management focussed on short term performance (and bonuses) and you have a potentially lethal situation because the results of the cheese paring and cost cutting will not be offset by advances in technology (Thanks to risk shifting), and in any case, the damage will not be visible for at least three to five years, by which time the culprits have taken their bonuses and are long gone.
So possums, I predict you are going to see more Congonhas, Medans, Adam Airs and Phukets as less experienced pilots, working longer hours, to tighter schedules, with minimal cabin crew, fly more sophisticated aircraft with minimum allowable maintenance performed by less experienced engineers into more and more destinations, in worse and worse weather.
To put it another way chaps, IT ALL ADDS UP, and it adds the wrong way.
The saddest part is that it is going to take not one, or three fatal accidents, but ten to fifteen in one year before regulatory bodies cannot ignore the truth.
You can cut too deep, but it won't be the managers who do it that bear the cost. It will be the flying public.
Problems with maintenance, training and experience levels do not simply appear overnight, it takes many many years of cost cutting and cheese paring to increase the probability of an unsafe situation developing into an accident.
Then of course you have Aircraft manufacturers designing in new technology that in theory increases safety levels.
However, there is a sad human phenomenon called "risk shifting", which is when the introduction of a safer technology is offset by increasing the level of risk in other areas, so that the total level of risk remains the same.
Best example I am aware of is ABS in cars, has it reduced the frequency of nose to tail crashes? Apparently not, because drivers compensate for better brakes by driving closer together.
Compound this situation by management focussed on short term performance (and bonuses) and you have a potentially lethal situation because the results of the cheese paring and cost cutting will not be offset by advances in technology (Thanks to risk shifting), and in any case, the damage will not be visible for at least three to five years, by which time the culprits have taken their bonuses and are long gone.
So possums, I predict you are going to see more Congonhas, Medans, Adam Airs and Phukets as less experienced pilots, working longer hours, to tighter schedules, with minimal cabin crew, fly more sophisticated aircraft with minimum allowable maintenance performed by less experienced engineers into more and more destinations, in worse and worse weather.
To put it another way chaps, IT ALL ADDS UP, and it adds the wrong way.
The saddest part is that it is going to take not one, or three fatal accidents, but ten to fifteen in one year before regulatory bodies cannot ignore the truth.
You can cut too deep, but it won't be the managers who do it that bear the cost. It will be the flying public.
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The training level of the pilots would be an interesting follow-up. I don't know much about the simulator curriculum, but I would imagine that pilots are rotated through simulator time as quickly as practical as part of the cost cutting regimen. Are airline pilots faced with go-round simulations on LCC's or are they run through like the proverbial sausage machine with just the checks required for recency experience?
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they carry the most and crash the least??
I would think that the Low Cost Carriers throughout the world would by now be carrying the MOST PASSENGERS and doing the MOST SECTORS....I don't see them going in like darts as some people would like to say....
Is Garuda(Surabaya) a LLC....is QF(Bangkok) a LLC...I think people should get out there and see what it is like ON-THE-LINE....language barriers...different cultures in the cockpit....atrocious weather etc etc etc....accidents can and will happen to any airline, unfortunately a fact of life like cars on the road.
and as for the article...well most probably written by a travel agent organisation who will not survive because the LLC don't pay commissions!! or was it funded by Star Alliance or Oneworld??
LLC are here to stay and big fat bloated over rated under serviced and over priced monopolistic airlines like our own kangaroo carcass will eventually disappear forever and not before time.
Why has Toyota got 35% of the North American market....better value for your dollar!!......no one is running around saying Toyota cars are unsafe!
Is Garuda(Surabaya) a LLC....is QF(Bangkok) a LLC...I think people should get out there and see what it is like ON-THE-LINE....language barriers...different cultures in the cockpit....atrocious weather etc etc etc....accidents can and will happen to any airline, unfortunately a fact of life like cars on the road.
and as for the article...well most probably written by a travel agent organisation who will not survive because the LLC don't pay commissions!! or was it funded by Star Alliance or Oneworld??
LLC are here to stay and big fat bloated over rated under serviced and over priced monopolistic airlines like our own kangaroo carcass will eventually disappear forever and not before time.
Why has Toyota got 35% of the North American market....better value for your dollar!!......no one is running around saying Toyota cars are unsafe!
emu787
And I suppose that is why 80% of LCC fail within the first five years of operation world wide. Have a look around, full service airlines are the ones making the really big profits. Profits their LCC cousins could only dream about.
And I suppose that is why 80% of LCC fail within the first five years of operation world wide. Have a look around, full service airlines are the ones making the really big profits. Profits their LCC cousins could only dream about.
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Sunfish,
Just to highlight a point, about perceptions and facts etc.....
The reason for this is simple, they may not have better brakes at all. ABS contrary to what many people think, does not make the brakes stop the vehicle any quicker, it just prevents you from over braking, locking a wheel and having reduced control. In some instances it can actually increase stopping distance.
It is as you point out, a way of shifting risk, and catering for drivers who who have lesser skills.
J
Just to highlight a point, about perceptions and facts etc.....
Best example I am aware of is ABS in cars, has it reduced the frequency of nose to tail crashes? Apparently not, because drivers compensate for better brakes by driving closer together.
It is as you point out, a way of shifting risk, and catering for drivers who who have lesser skills.
J
Jabawocky
Ah that isn’t strictly correct. With ABS (Anti Skid Brakes) working, pushing the brakes as hard as you can will stop the car in the shortest distance by maintaining just enough traction, i.e. on the verge of a skid by pulsating the brakes rapidly on and off. Very few drivers would be able to apply maximum breaking without ABS and not skid. As soon as you start skidding, the stopping distance increases. Hence the safety aspect of ABS.
ABS contrary to what many people think, does not make the brakes stop the vehicle any quicker, it just prevents you from over braking, locking a wheel and having reduced control. In some instances it can actually increase stopping distance.
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Have a look around, full service airlines are the ones making the really big profits. Profits their LCC cousins could only dream about.
80% of the LCC market here is made up by 20% of the airlines
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Diverging - when in rome...
A typical ABS is composed of a central electronic unit, four speed sensors (one for each wheel), and two or more hydraulic valves on the brake circuit. The electronic unit constantly monitors the rotation speed of each wheel. When it senses that any number of wheels are rotating considerably slower than the others (a condition that will bring it to lock) it moves the valves to decrease the pressure on the braking circuit, effectively reducing the braking force on that wheel. The wheel(s) then turn faster and when they turn too fast, the force is reapplied. This process is repeated continuously, and this causes the characteristic pulsing feel through the brake pedal. A typical anti-lock system can apply and release braking pressure up to 20 times a second.
And who is the next person who wants to have a guess?
Jabawocky is quite correct. ABS was introduced in the hope of reducing loss of steering control during heavy braking conditions.
There are many misconceptions about ABS. One of them is that the car will always stop in a much shorter distance, every time. The only reason they became available on mass produced small vehicles is that brake technology finally caught up with the weight of most vehicles, and now we have much smaller and lighter vehicles on the road than we did 30 years ago.
The brakes are not "pulsated" on and off. Each wheel individually has the fluid pressure being supplied to it momentarily reduced to allow the wheel to regain RPM and therefore traction before the ABS solenoid then allows brake fluid under the drivers pressure control resume pressure to the caliper. This happens when the ABS control unit (via an RPM sensor on all wheels) picks up a %age of underspeed on one wheel in relation to the other wheels RPM. The control unit for the system constantly compares wheel RPM and only makes adjustments or inputs when a certain discrepancy in RPM is detected over a certain braking value. The idea is to allow steering inputs to help the driver steer themselves out of trouble without locking the inside wheel of a swerving car etc.
In actual fact most vehicles fitted with ABS will take longer to stop on anything other than slippery wet bitumen or ice than those able to hold an "almost locked-up" condition. However as 404 very correctly pointed out, this is beyond the scope of many drivers to be able to do and keep the vehicle in balance enough not to lose it while manouvring around something under max braking.
404. A "skidding" car on loose gravel pulling up in a straight line will pull-up faster than one will with ABS. The reason? The skidding front tyres (taking around 80+% of the vehicles weight under heavy braking) will form a bow wave and cut down through the gravel and get to the harder, higher friction coefficient surface below. Rotating wheels continue to let loose gravel interfere with traction. The best way to see the effect of ABS is to slip two wheels off the bitumen onto a loose gravel shoulder and hit the picks hard. You'll get the idea.
I hope that settles that, end of thread drift. The problems with tarring all LCC with that brush of generic minimum low standards is that it is the regulator(s) that set minimum standards, not the LCC. If the LCC is serious about safety, they'll come up with something that fulfils their requirements and obligations under the law and hopefully is a step above the minimum.
Jabawocky is quite correct. ABS was introduced in the hope of reducing loss of steering control during heavy braking conditions.
There are many misconceptions about ABS. One of them is that the car will always stop in a much shorter distance, every time. The only reason they became available on mass produced small vehicles is that brake technology finally caught up with the weight of most vehicles, and now we have much smaller and lighter vehicles on the road than we did 30 years ago.
The brakes are not "pulsated" on and off. Each wheel individually has the fluid pressure being supplied to it momentarily reduced to allow the wheel to regain RPM and therefore traction before the ABS solenoid then allows brake fluid under the drivers pressure control resume pressure to the caliper. This happens when the ABS control unit (via an RPM sensor on all wheels) picks up a %age of underspeed on one wheel in relation to the other wheels RPM. The control unit for the system constantly compares wheel RPM and only makes adjustments or inputs when a certain discrepancy in RPM is detected over a certain braking value. The idea is to allow steering inputs to help the driver steer themselves out of trouble without locking the inside wheel of a swerving car etc.
In actual fact most vehicles fitted with ABS will take longer to stop on anything other than slippery wet bitumen or ice than those able to hold an "almost locked-up" condition. However as 404 very correctly pointed out, this is beyond the scope of many drivers to be able to do and keep the vehicle in balance enough not to lose it while manouvring around something under max braking.
404. A "skidding" car on loose gravel pulling up in a straight line will pull-up faster than one will with ABS. The reason? The skidding front tyres (taking around 80+% of the vehicles weight under heavy braking) will form a bow wave and cut down through the gravel and get to the harder, higher friction coefficient surface below. Rotating wheels continue to let loose gravel interfere with traction. The best way to see the effect of ABS is to slip two wheels off the bitumen onto a loose gravel shoulder and hit the picks hard. You'll get the idea.
I hope that settles that, end of thread drift. The problems with tarring all LCC with that brush of generic minimum low standards is that it is the regulator(s) that set minimum standards, not the LCC. If the LCC is serious about safety, they'll come up with something that fulfils their requirements and obligations under the law and hopefully is a step above the minimum.
ABS allows you to maintain controllability but does not stop you the quickest... but what the hell are we talking about ABS for???
Its simple, LCC's fail within the first 5 years because their profit margins are smaller and any inefficiencies in the system cause productivity reduction. 22 min turn around time is a bit tight, but I'm hoping that also means their on-time performance is poor. As for 10 hours of utilisation a day, this is required for a LCC's operations. Economies of scale require it. Profits are made through capacity, not individual seat costs.
But the biggest issue here is safety. An increase in accidents by low costs carriers is unfortunately a given because of the fact that they are flying increasingly more sectors comparatively. Thorough oversight must be sought by the regulator to avoid corners being cut. COrrect management must steer these organisation in the correct direction.
I don't like how this article uses a common umbrella for all LCC's. Would you throw Garuda and Qantas into the same group, especially when considering safety? How hard is it to get people that know aviation to write these articles.....
Its simple, LCC's fail within the first 5 years because their profit margins are smaller and any inefficiencies in the system cause productivity reduction. 22 min turn around time is a bit tight, but I'm hoping that also means their on-time performance is poor. As for 10 hours of utilisation a day, this is required for a LCC's operations. Economies of scale require it. Profits are made through capacity, not individual seat costs.
But the biggest issue here is safety. An increase in accidents by low costs carriers is unfortunately a given because of the fact that they are flying increasingly more sectors comparatively. Thorough oversight must be sought by the regulator to avoid corners being cut. COrrect management must steer these organisation in the correct direction.
I don't like how this article uses a common umbrella for all LCC's. Would you throw Garuda and Qantas into the same group, especially when considering safety? How hard is it to get people that know aviation to write these articles.....
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I hope that settles that, end of thread drift. The problems with tarring all LCC with that brush of generic minimum low standards is that it is the regulator(s) that set minimum standards, not the LCC. If the LCC is serious about safety, they'll come up with something that fulfils their requirements and obligations under the law and hopefully is a step above the minimum.
An increase in accidents by low costs carriers is unfortunately a given because of the fact that they are flying increasingly more sectors comparatively
h, its an unfortunate truth. The accident rate at present is 0.05 per million departures and has remained at that level for years. infact in recent years it has increased. But why? Thats a topic for another time and place. With an increase in the amount of sectors flown globally, the hull loss rate will no increase but the number of aircraft crashes will. In twenty years at the current rate of growth the traveling public will expect to hear of a hull-loss each and every week.
Scary isn't it, unfortunately the numbers are not on the industries side.
The risk of having an accident will not increase, infact there is probably a decreased risk over time due to advancement in technology, maintenance, HF awareness and ergonomics etc..... but the number of accidents will increase.
Scary isn't it, unfortunately the numbers are not on the industries side.
The risk of having an accident will not increase, infact there is probably a decreased risk over time due to advancement in technology, maintenance, HF awareness and ergonomics etc..... but the number of accidents will increase.
Bula
I think as the aircraft came off the end of a runway in wet conditions, talking about Anti-skid is relevant. I will concede though that there are differences in ABS on cars and anti-skid systems on aircraft. The general principal of how they work though is the same.
OpsNormal
I should have probably stated that on a wet or slippery surface ABS brakes will work better than conventional brakes in stopping the car in the shortest possible distance. On a dry road the distances should be about the same. On gravel, slush and uncompacted snow the ABS system as you have said will take longer to stop the car because it will ride on top of the contaminant instead of producing a bow wave in front of the tires as would happen on a car with conventional brakes. ABS does work by rapidly applying and taking away brake pressure to the relevant tires that are on the verge of skidding to maintain traction. This is noted by a rapid and loud pulsating through the brake pedals of most vehicles.
I think as the aircraft came off the end of a runway in wet conditions, talking about Anti-skid is relevant. I will concede though that there are differences in ABS on cars and anti-skid systems on aircraft. The general principal of how they work though is the same.
OpsNormal
I should have probably stated that on a wet or slippery surface ABS brakes will work better than conventional brakes in stopping the car in the shortest possible distance. On a dry road the distances should be about the same. On gravel, slush and uncompacted snow the ABS system as you have said will take longer to stop the car because it will ride on top of the contaminant instead of producing a bow wave in front of the tires as would happen on a car with conventional brakes. ABS does work by rapidly applying and taking away brake pressure to the relevant tires that are on the verge of skidding to maintain traction. This is noted by a rapid and loud pulsating through the brake pedals of most vehicles.
The ABS System
The theory behind anti-lock brakes is simple. A skidding wheel (where the tire contact patch is sliding relative to the road) has less traction than a non-skidding wheel. If you have been stuck on ice, you know that if your wheels are spinning you have no traction. This is because the contact patch is sliding relative to the ice. By keeping the wheels from skidding while you slow down, anti-lock brakes benefit you in two ways:
1. You'll stop faster, and
2. You'll be able to steer while you stop.
There are four main components to an ABS system:
1. Speed sensors
2. Pump
3. Valves
4. Controller
Speed Sensors
The anti-lock braking system needs some way of knowing when a wheel is about to lock up. The speed sensors, which are located at each wheel, or in some cases in the differential, provide this information.
Valves
There is a valve in the brake line of each brake controlled by the ABS. On some systems, the valve has three positions:
• In position one, the valve is open; pressure from the master cylinder is passed right through to the brake.
• In position two, the valve blocks the line, isolating that brake from the master cylinder. This prevents the pressure from rising further should the driver push the brake pedal harder.
• In position three, the valve releases some of the pressure from the brake.
Pump
Since the valve is able to release pressure from the brakes, there has to be some way to put that pressure back. That is what the pump does; when a valve reduces the pressure in a line, the pump is there to get the pressure back up.
Controller
The controller is a computer in the car. It watches the speed sensors and controls the valves.
ABS at Work
In a car fitted with ABS, the controller monitors the speed sensors at all times. It is looking for decelerations in the wheel that are out of the ordinary. Right before a wheel locks up, it will experience a rapid deceleration. If left unchecked, the wheel would stop much more quickly than any car could. It might take a car five seconds to stop from 60 mph (96.6 kph) under ideal conditions, but a wheel that locks up could stop spinning in less than a second.
The ABS controller knows that such a rapid deceleration is impossible, so it reduces the pressure to that brake until it sees an acceleration, then it increases the pressure until it sees the deceleration again. It can do this very quickly, before the tire can actually significantly change speed. The result is that the tire slows down at the same rate as the car, with the brakes keeping the tires very near the point at which they will start to lock up. This gives the system maximum braking power.
When the ABS system is in operation you will feel a pulsing in the brake pedal; this comes from the rapid opening and closing of the valves. Some ABS systems can cycle up to 15 times per second.
Anti-Lock Brake Types
Anti-lock braking systems use different schemes depending on the type of brakes in use. We will refer to them by the number of channels -- that is, how many valves that are individually controlled -- and the number of speed sensors.
• Four-channel, four-sensor ABS - This is the best scheme. There is a speed sensor on all four wheels and a separate valve for all four wheels. With this setup, the controller monitors each wheel individually to make sure it is achieving maximum braking force.
• Three-channel, three-sensor ABS - This scheme, commonly found on pickup trucks with four-wheel ABS, has a speed sensor and a valve for each of the front wheels, with one valve and one sensor for both rear wheels. The speed sensor for the rear wheels is located in the rear axle.
This system provides individual control of the front wheels, so they can both achieve maximum braking force. The rear wheels, however, are monitored together; they both have to start to lock up before the ABS will activate on the rear. With this system, it is possible that one of the rear wheels will lock during a stop, reducing brake effectiveness.
• One-channel, one-sensor ABS - This system is commonly found on pickup trucks with rear-wheel ABS. It has one valve, which controls both rear wheels, and one speed sensor, located in the rear axle.
This system operates the same as the rear end of a three-channel system. The rear wheels are monitored together and they both have to start to lock up before the ABS kicks in. In this system it is also possible that one of the rear wheels will lock, reducing brake effectiveness.
This system is easy to identify. Usually there will be one brake line going through a T-fitting to both rear wheels. You can locate the speed sensor by looking for an electrical connection near the differential on the rear-axle housing.
ABS Facts
• ABS is designed to help the driver maintain control of the vehicle during emergency braking situations, not make the car stop more quickly. ABS generally shorten stopping distances on wet or slippery roads and many systems will shorten stopping distances on dry roads. On very soft surfaces, such as loose gravel or unpacked snow, an ABS system may actually lengthen stopping distances. In wet or slippery conditions, you should still make sure you drive carefully, always keep a safe distance behind the vehicle in front of you, and maintain a speed consistent with the road conditions.
The theory behind anti-lock brakes is simple. A skidding wheel (where the tire contact patch is sliding relative to the road) has less traction than a non-skidding wheel. If you have been stuck on ice, you know that if your wheels are spinning you have no traction. This is because the contact patch is sliding relative to the ice. By keeping the wheels from skidding while you slow down, anti-lock brakes benefit you in two ways:
1. You'll stop faster, and
2. You'll be able to steer while you stop.
There are four main components to an ABS system:
1. Speed sensors
2. Pump
3. Valves
4. Controller
Speed Sensors
The anti-lock braking system needs some way of knowing when a wheel is about to lock up. The speed sensors, which are located at each wheel, or in some cases in the differential, provide this information.
Valves
There is a valve in the brake line of each brake controlled by the ABS. On some systems, the valve has three positions:
• In position one, the valve is open; pressure from the master cylinder is passed right through to the brake.
• In position two, the valve blocks the line, isolating that brake from the master cylinder. This prevents the pressure from rising further should the driver push the brake pedal harder.
• In position three, the valve releases some of the pressure from the brake.
Pump
Since the valve is able to release pressure from the brakes, there has to be some way to put that pressure back. That is what the pump does; when a valve reduces the pressure in a line, the pump is there to get the pressure back up.
Controller
The controller is a computer in the car. It watches the speed sensors and controls the valves.
ABS at Work
In a car fitted with ABS, the controller monitors the speed sensors at all times. It is looking for decelerations in the wheel that are out of the ordinary. Right before a wheel locks up, it will experience a rapid deceleration. If left unchecked, the wheel would stop much more quickly than any car could. It might take a car five seconds to stop from 60 mph (96.6 kph) under ideal conditions, but a wheel that locks up could stop spinning in less than a second.
The ABS controller knows that such a rapid deceleration is impossible, so it reduces the pressure to that brake until it sees an acceleration, then it increases the pressure until it sees the deceleration again. It can do this very quickly, before the tire can actually significantly change speed. The result is that the tire slows down at the same rate as the car, with the brakes keeping the tires very near the point at which they will start to lock up. This gives the system maximum braking power.
When the ABS system is in operation you will feel a pulsing in the brake pedal; this comes from the rapid opening and closing of the valves. Some ABS systems can cycle up to 15 times per second.
Anti-Lock Brake Types
Anti-lock braking systems use different schemes depending on the type of brakes in use. We will refer to them by the number of channels -- that is, how many valves that are individually controlled -- and the number of speed sensors.
• Four-channel, four-sensor ABS - This is the best scheme. There is a speed sensor on all four wheels and a separate valve for all four wheels. With this setup, the controller monitors each wheel individually to make sure it is achieving maximum braking force.
• Three-channel, three-sensor ABS - This scheme, commonly found on pickup trucks with four-wheel ABS, has a speed sensor and a valve for each of the front wheels, with one valve and one sensor for both rear wheels. The speed sensor for the rear wheels is located in the rear axle.
This system provides individual control of the front wheels, so they can both achieve maximum braking force. The rear wheels, however, are monitored together; they both have to start to lock up before the ABS will activate on the rear. With this system, it is possible that one of the rear wheels will lock during a stop, reducing brake effectiveness.
• One-channel, one-sensor ABS - This system is commonly found on pickup trucks with rear-wheel ABS. It has one valve, which controls both rear wheels, and one speed sensor, located in the rear axle.
This system operates the same as the rear end of a three-channel system. The rear wheels are monitored together and they both have to start to lock up before the ABS kicks in. In this system it is also possible that one of the rear wheels will lock, reducing brake effectiveness.
This system is easy to identify. Usually there will be one brake line going through a T-fitting to both rear wheels. You can locate the speed sensor by looking for an electrical connection near the differential on the rear-axle housing.
ABS Facts
• ABS is designed to help the driver maintain control of the vehicle during emergency braking situations, not make the car stop more quickly. ABS generally shorten stopping distances on wet or slippery roads and many systems will shorten stopping distances on dry roads. On very soft surfaces, such as loose gravel or unpacked snow, an ABS system may actually lengthen stopping distances. In wet or slippery conditions, you should still make sure you drive carefully, always keep a safe distance behind the vehicle in front of you, and maintain a speed consistent with the road conditions.
Join Date: Jul 2007
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404Titan
I do not agree with you entirely and even the evidence of your own post above agrees with my point.............
So I think you may now see my point. I have experience racing cars, with and without. I have also done some experiments on the beach, and PROVEN beyond doubt a very significant difference when stopping quickly on sand. To the point my new LC100 will get ABS disconnected every time I go on the beach in future.
J
NOTE: Anti skid like on your B777 etc is different application, and especially on wet runways.
I do not agree with you entirely and even the evidence of your own post above agrees with my point.............
ABS Facts
• ABS is designed to help the driver maintain control of the vehicle during emergency braking situations, not make the car stop more quickly. ABS generally shorten stopping distances on wet or slippery roads and many systems will shorten stopping distances on dry roads. On very soft surfaces, such as loose gravel or unpacked snow, an ABS system may actually lengthen stopping distances. In wet or slippery conditions, you should still make sure you drive carefully, always keep a safe distance behind the vehicle in front of you, and maintain a speed consistent with the road conditions.
• ABS is designed to help the driver maintain control of the vehicle during emergency braking situations, not make the car stop more quickly. ABS generally shorten stopping distances on wet or slippery roads and many systems will shorten stopping distances on dry roads. On very soft surfaces, such as loose gravel or unpacked snow, an ABS system may actually lengthen stopping distances. In wet or slippery conditions, you should still make sure you drive carefully, always keep a safe distance behind the vehicle in front of you, and maintain a speed consistent with the road conditions.
J
NOTE: Anti skid like on your B777 etc is different application, and especially on wet runways.
Jabawocky
I think you will find in my post that I don’t disagree with you. ABS is installed in motor vehicles to maintain controllability in emergency braking situations. A secondary effect is its ability to stop a car in a shorter distance than conventional braked cars on wet or slippery sealed (I didn't say it but I was implying it) roads and in most cases at least the same distance on dry sealed road.
That is why I said:
Whether it is gravel, sand or uncompacted snow, exactly same principal applies.
You have no disagreement with me here either. I made a quote saying just this as well:
I think you will find in my post that I don’t disagree with you. ABS is installed in motor vehicles to maintain controllability in emergency braking situations. A secondary effect is its ability to stop a car in a shorter distance than conventional braked cars on wet or slippery sealed (I didn't say it but I was implying it) roads and in most cases at least the same distance on dry sealed road.
I have also done some experiments on the beach, and PROVEN beyond doubt a very significant difference when stopping quickly on sand.
On gravel, slush and uncompacted snow the ABS system as you have said will take longer to stop the car because it will ride on top of the contaminant instead of producing a bow wave in front of the tires as would happen on a car with conventional brakes.
Anti skid like on your B777 etc is different application, and especially on wet runways.
I will concede though that there are differences in ABS on cars and anti-skid systems on aircraft. The general principal of how they work though is the same.
