B777 over the atlantic
Guest
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B777 over the atlantic
dear all
now heres the scenario, your a pilot of a B777 and your half way over the atlantic, or basically beyond the point of return.
Theres an engine failure, what would be the procedure and would u be able to continue on one engine and for how long?
as with the B747/A340 or any other 4 engine a/c u could continue as u have three engines to rely on in an event of engine failure so surely on that principle atlantic flights should be 4 engined a/c.
i know that 777 engines produce more thrust then 747s being 100,000lbs and 60,000lbs respectively but crossing terrain where there is little chance of making an emergency landing warrants 4 engines if the above principle is correct.
any answers would be welecome.
now heres the scenario, your a pilot of a B777 and your half way over the atlantic, or basically beyond the point of return.
Theres an engine failure, what would be the procedure and would u be able to continue on one engine and for how long?
as with the B747/A340 or any other 4 engine a/c u could continue as u have three engines to rely on in an event of engine failure so surely on that principle atlantic flights should be 4 engined a/c.
i know that 777 engines produce more thrust then 747s being 100,000lbs and 60,000lbs respectively but crossing terrain where there is little chance of making an emergency landing warrants 4 engines if the above principle is correct.
any answers would be welecome.
Guest
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To: purple haze
If I understand it correctly the aircraft must be within X minutes of an alternate in the event of a single engine failure. As a part of the certification the 777 had to demonstrate this capability and the capability of operating on one engine for an extended period of time. Also, the engines had to demonstrate a certain level of reliability. It was my understanding that the 777 was granted ETOPS right out of the box because of how it was designed. The probability of losing a second engine is quite small unless the first engine failed due to a fuel problem, which can also effect the second engine.
Several years ago the president of Airbus Industries was giving a speech in the US in order to promote ETOPS for the A310. He too reflected on the probability of losing two engines on a two engine aircraft were highly remote or in probability language 1 10-9 or one time in a billion.
Within a very short time a Canadian 767 almost crashed when both engines flamed out due to fuel starvation. The same thing happened to two DC-9s and a DC-10. Shortly after that an L-1011 almost crashed due to oil starvation in all three engines due to a maintenance error. And, how about the 747 that lost all four engines when the plane flew through a cloud of volcanic ash.
I would dammed well imagine that even though the 777 is certified ETOPS the pilots pucker factor will go up by several orders of magnitude when his first engine fails.
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The Cat
If I understand it correctly the aircraft must be within X minutes of an alternate in the event of a single engine failure. As a part of the certification the 777 had to demonstrate this capability and the capability of operating on one engine for an extended period of time. Also, the engines had to demonstrate a certain level of reliability. It was my understanding that the 777 was granted ETOPS right out of the box because of how it was designed. The probability of losing a second engine is quite small unless the first engine failed due to a fuel problem, which can also effect the second engine.
Several years ago the president of Airbus Industries was giving a speech in the US in order to promote ETOPS for the A310. He too reflected on the probability of losing two engines on a two engine aircraft were highly remote or in probability language 1 10-9 or one time in a billion.
Within a very short time a Canadian 767 almost crashed when both engines flamed out due to fuel starvation. The same thing happened to two DC-9s and a DC-10. Shortly after that an L-1011 almost crashed due to oil starvation in all three engines due to a maintenance error. And, how about the 747 that lost all four engines when the plane flew through a cloud of volcanic ash.
I would dammed well imagine that even though the 777 is certified ETOPS the pilots pucker factor will go up by several orders of magnitude when his first engine fails.
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The Cat
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Cat
1 in a billion is a patently absurd estimation, the guy deserves to be ridiculed. It is exactly this type of estimating that was so criticised in the Challenger Inquiry. It in fact means you could fly a flight a day and not have a failure in nearly 3 million years. Not very likely. People really ought to chalenge these estimates moer often.
1 in a billion is a patently absurd estimation, the guy deserves to be ridiculed. It is exactly this type of estimating that was so criticised in the Challenger Inquiry. It in fact means you could fly a flight a day and not have a failure in nearly 3 million years. Not very likely. People really ought to chalenge these estimates moer often.
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To: Junior Jet Clubber
Contact me via email and i will provide you with information relative to your comments.
What you described is exactly how they prove the certification of commercial aircraft. They manipulate meaningless numbers until it can be proven that the aircraft systems meet the specified JAR and FAA requirements for safety. The 1 10-9 figure was established by the FAA and has been adopted by the CAA, LBA,DGCA and are incorporated in the JARs.
Regarding the Challenger, on the 604 they proved that some of the systems had a safety number of in excess of 1 10-12
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The Cat
Contact me via email and i will provide you with information relative to your comments.
What you described is exactly how they prove the certification of commercial aircraft. They manipulate meaningless numbers until it can be proven that the aircraft systems meet the specified JAR and FAA requirements for safety. The 1 10-9 figure was established by the FAA and has been adopted by the CAA, LBA,DGCA and are incorporated in the JARs.
Regarding the Challenger, on the 604 they proved that some of the systems had a safety number of in excess of 1 10-12
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The Cat
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Purple Haze:
One of the problems you run into here is that each of the system components (engine, fuel system, etc) is so highly reliable that when you put them together the mathmatics used in the usual reliability calculations of mean time between failure and such become meaningless because (among other reasons) the numbers plugged into the equations are all estimates. This is because it takes so long (calendar time) to develop a data set.
If you are not comfortable with the "9 nines" reliability of the engine reflect on the fact that the navigation system (GPS) has "7 nines" as a design goal (to be demonstrated..it will take a couple more years to collect enough data) so your engine may work but you won't know where you are unless you take along your boy scout compass.
One of the problems you run into here is that each of the system components (engine, fuel system, etc) is so highly reliable that when you put them together the mathmatics used in the usual reliability calculations of mean time between failure and such become meaningless because (among other reasons) the numbers plugged into the equations are all estimates. This is because it takes so long (calendar time) to develop a data set.
If you are not comfortable with the "9 nines" reliability of the engine reflect on the fact that the navigation system (GPS) has "7 nines" as a design goal (to be demonstrated..it will take a couple more years to collect enough data) so your engine may work but you won't know where you are unless you take along your boy scout compass.
Guest
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Whatever calculations you make, they can only be based on factors you can think of that have a significant impact in the process.
It takes only a flock of birds or a uncontained engine failure with the pieces all over the place to have significant damage on both engines.
Fly the B 777 or any twin for that matter into some african destinations and you will see that the nine number figure does not stand up anymore.
Good Luck
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Smooth Trimmer
[This message has been edited by Streamline (edited 05 January 2001).]
[This message has been edited by Streamline (edited 05 January 2001).]
It takes only a flock of birds or a uncontained engine failure with the pieces all over the place to have significant damage on both engines.
Fly the B 777 or any twin for that matter into some african destinations and you will see that the nine number figure does not stand up anymore.
Good Luck
------------------
Smooth Trimmer
[This message has been edited by Streamline (edited 05 January 2001).]
[This message has been edited by Streamline (edited 05 January 2001).]
Guest
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To: Streamline
The initial numbers to establish reliability are taken from the failure rate databases of the company making the component or the aircraft. In many cases even the largest of aircraft manufacturers don’t have a failure rate database. In cases like that the reliability engineers will get failure rates from other sources. Many reliability engineers (like myself) will accumulate their own failure rates from various jobs they have worked. The US Air Force has an extensive data base for electronic equipment that is based on the projected and demonstrated failure histories of thousands of commonly used electronic parts ranging from a diode to the most complex LSI chip.
Failure rates for mechanical equipment and piece parts are another story. That data that is available does not reflect the specific usage for the piece parts in that data base. In cases like that the analyst must provide some K factor that will allow him/her to calculate the failure rate by multiplying the failure rate by the K factor. It is far from accurate but that is how they arrive at the part predicted rate of failure (MTBF).
The analyst creates a block diagram replicating the piece part relationship within the item under analysis. The failure rate numbers are plugged into the individual blocks and the reliability and unreliability numbers are factored from the failure rates of each piece part and that number is also plugged into the respective blocks. Assuming the unit under analysis would fail its’ function if any of the blocks failed it is considered to be a series block diagram. To get the reliability number for the unit the individual numbers in the series are multiplied. The reliability numbers are a decimal point followed by a series of 9s. The numbers are plugged into calculator or a computer and then chain multiplied. The answer is a series of 9s followed by other numbers that are less than 9.
Now, the problems begin. First of all, how accurate are the numbers and do the numbers really represent the inherent failure rates for the parts? When the concept of reliability was first started by the USAF it was to establish the reliability of electronic black boxes. The function of the block diagram was to provide a performance number. By calculating the basic reliability of the black box they could then plug in numbers representing a different part or parts and run the calculation again to determine the effects of the parts change on the predicted reliability of the black box.
There were other types of block diagrams representing very complex and multiple redundancies. If you had a complex or parallel circuit a calculation was performed to establish the reliability of that circuit. That calculation provided a decimal point followed by as many a 12 9s and it was given a reliability of 1 so that in a chain calculation it would have no effect on the ultimate number.
I previously stated that the block diagram concept was to provide comparative performance numbers. Not now. Now they are used to calculate the reliability of the black box and compare it to the required MTBF established by the customer. By selecting the right numbers the reliability requirements were always met. When they applied this concept to mechanical systems the whole thing fell apart due to the lack of reliable failure rate data. I have been doing this since 1968 and it still hasn’t changed.
Now it gets worse. To certify an aircraft it must be proven that the systems meet the probabilities of failure as established by the certification authorities. To do this a fault tree or Systems Safety Analysis must be performed. This is usually in the form of a series of gates arranged to reflect the inter relationship of the components in the system. There are usually AND gates and OR gates. The gates can be visualized like a door with many locks or a door with only one lock. An AND gate has many locks and an OR gate has only one lock. Once the diagram is established it is then determined what must fail in order to lose a function and possibly have an adverse effect on the next higher level.
Lines representing an individual failure that can effect another part of the system connect the various gates. Assume that you have an OR gate with five lines connected to it. Any one of those failures has a key that will open the lock and allow the door to be opened thus passing the failure to the next higher level. Now, assume that the AND gate has five lines connected to it. In order to open the door, all five keys must be used in order for those collective failures to be manifested at a higher level. This combination of AND / OR gates goes upward and terminates at an AND gate which is the highest level in the system. The closer to the top the more AND gate and fewer OR gates.
After constructing the diagram the analyst must determine the probability of total failure of the system. To do this he uses Boolean Algebra to make the calculations. Assuming an OR gate with five inputs the analyst will add the failure rates that were derived from the block diagram to calculate the total failure rate for that gate. One line passes from that gate to the next higher level and the calculated failure rate for that gate is assigned to the line and it in turn passes to the next level and hits another gate. If that gate is an OR gate with several lines connected to it the same calculation is performed and so on. If the bottom gate is an AND gate with five inputs the individual failure rates are multiplied in the same manner as the chain calculations in the reliability block diagram. The line passing out of that gate is assigned the probability of failure for the gate and passes upward just like the OR gate described previously. When all of the lines terminate at the top AND gate a calculation is made and the product of that calculation for the failure probability for that system. It must be 1 10-9 or better. In most cases it is proved to be even better.
Now, ask yourself how reliable is this number if it is based on meaningless numbers that are not representative of the parts that are reflected by those numbers. But that isn’t all. The top numbers that represent the probability of failure represent the systems on the aircraft and not the aircraft. In order to determine the probability of the loss of the aircraft it would be necessary to take the individual top gates and connect them into an OR gate which represents the aircraft. If you would perform the same calculation for an OR gate the aircraft would have a probability of loss well below 1 10-9. The FAA does not require this last calculation because it will prove that the aircraft does not meet the requirements set up for the systems. Even if the numbers that went into the various calculations were true representations of the parts failure rates the answer to the final calculation would be the same. The aircraft cannot meet the FAA, CAA, LBA, DGCA and JAR requirements and it doesn’t make any difference who makes the plane.
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The Cat
The initial numbers to establish reliability are taken from the failure rate databases of the company making the component or the aircraft. In many cases even the largest of aircraft manufacturers don’t have a failure rate database. In cases like that the reliability engineers will get failure rates from other sources. Many reliability engineers (like myself) will accumulate their own failure rates from various jobs they have worked. The US Air Force has an extensive data base for electronic equipment that is based on the projected and demonstrated failure histories of thousands of commonly used electronic parts ranging from a diode to the most complex LSI chip.
Failure rates for mechanical equipment and piece parts are another story. That data that is available does not reflect the specific usage for the piece parts in that data base. In cases like that the analyst must provide some K factor that will allow him/her to calculate the failure rate by multiplying the failure rate by the K factor. It is far from accurate but that is how they arrive at the part predicted rate of failure (MTBF).
The analyst creates a block diagram replicating the piece part relationship within the item under analysis. The failure rate numbers are plugged into the individual blocks and the reliability and unreliability numbers are factored from the failure rates of each piece part and that number is also plugged into the respective blocks. Assuming the unit under analysis would fail its’ function if any of the blocks failed it is considered to be a series block diagram. To get the reliability number for the unit the individual numbers in the series are multiplied. The reliability numbers are a decimal point followed by a series of 9s. The numbers are plugged into calculator or a computer and then chain multiplied. The answer is a series of 9s followed by other numbers that are less than 9.
Now, the problems begin. First of all, how accurate are the numbers and do the numbers really represent the inherent failure rates for the parts? When the concept of reliability was first started by the USAF it was to establish the reliability of electronic black boxes. The function of the block diagram was to provide a performance number. By calculating the basic reliability of the black box they could then plug in numbers representing a different part or parts and run the calculation again to determine the effects of the parts change on the predicted reliability of the black box.
There were other types of block diagrams representing very complex and multiple redundancies. If you had a complex or parallel circuit a calculation was performed to establish the reliability of that circuit. That calculation provided a decimal point followed by as many a 12 9s and it was given a reliability of 1 so that in a chain calculation it would have no effect on the ultimate number.
I previously stated that the block diagram concept was to provide comparative performance numbers. Not now. Now they are used to calculate the reliability of the black box and compare it to the required MTBF established by the customer. By selecting the right numbers the reliability requirements were always met. When they applied this concept to mechanical systems the whole thing fell apart due to the lack of reliable failure rate data. I have been doing this since 1968 and it still hasn’t changed.
Now it gets worse. To certify an aircraft it must be proven that the systems meet the probabilities of failure as established by the certification authorities. To do this a fault tree or Systems Safety Analysis must be performed. This is usually in the form of a series of gates arranged to reflect the inter relationship of the components in the system. There are usually AND gates and OR gates. The gates can be visualized like a door with many locks or a door with only one lock. An AND gate has many locks and an OR gate has only one lock. Once the diagram is established it is then determined what must fail in order to lose a function and possibly have an adverse effect on the next higher level.
Lines representing an individual failure that can effect another part of the system connect the various gates. Assume that you have an OR gate with five lines connected to it. Any one of those failures has a key that will open the lock and allow the door to be opened thus passing the failure to the next higher level. Now, assume that the AND gate has five lines connected to it. In order to open the door, all five keys must be used in order for those collective failures to be manifested at a higher level. This combination of AND / OR gates goes upward and terminates at an AND gate which is the highest level in the system. The closer to the top the more AND gate and fewer OR gates.
After constructing the diagram the analyst must determine the probability of total failure of the system. To do this he uses Boolean Algebra to make the calculations. Assuming an OR gate with five inputs the analyst will add the failure rates that were derived from the block diagram to calculate the total failure rate for that gate. One line passes from that gate to the next higher level and the calculated failure rate for that gate is assigned to the line and it in turn passes to the next level and hits another gate. If that gate is an OR gate with several lines connected to it the same calculation is performed and so on. If the bottom gate is an AND gate with five inputs the individual failure rates are multiplied in the same manner as the chain calculations in the reliability block diagram. The line passing out of that gate is assigned the probability of failure for the gate and passes upward just like the OR gate described previously. When all of the lines terminate at the top AND gate a calculation is made and the product of that calculation for the failure probability for that system. It must be 1 10-9 or better. In most cases it is proved to be even better.
Now, ask yourself how reliable is this number if it is based on meaningless numbers that are not representative of the parts that are reflected by those numbers. But that isn’t all. The top numbers that represent the probability of failure represent the systems on the aircraft and not the aircraft. In order to determine the probability of the loss of the aircraft it would be necessary to take the individual top gates and connect them into an OR gate which represents the aircraft. If you would perform the same calculation for an OR gate the aircraft would have a probability of loss well below 1 10-9. The FAA does not require this last calculation because it will prove that the aircraft does not meet the requirements set up for the systems. Even if the numbers that went into the various calculations were true representations of the parts failure rates the answer to the final calculation would be the same. The aircraft cannot meet the FAA, CAA, LBA, DGCA and JAR requirements and it doesn’t make any difference who makes the plane.
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The Cat
Guest
Posts: n/a
To: BIK_116.80
You may be totally correct. When I read his post I was thinking about the Challenger that crashed in the states a month or so ago.
Now, if you want to know what I think really happened on the NASA Challenger just post your approval and I'll let you in on a technical matter that was never brought up in the investigation and if it was, it was hushed up.
Of course it will take the thread in another direction.
Incidently, one of the Women killed in the explosion was my nieces best girl friend and they were room mates in college.
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The Cat
You may be totally correct. When I read his post I was thinking about the Challenger that crashed in the states a month or so ago.
Now, if you want to know what I think really happened on the NASA Challenger just post your approval and I'll let you in on a technical matter that was never brought up in the investigation and if it was, it was hushed up.
Of course it will take the thread in another direction.
Incidently, one of the Women killed in the explosion was my nieces best girl friend and they were room mates in college.
------------------
The Cat
Guest
Posts: n/a
To: gaunty
To:
Regarding the Challenger explosion this is what the public was told. An “O” ring failed and allowed hot gasses and eventually a high velocity flame jet to escape past the defective “O” ring and impinge on the composite fuel and oxidizer tank resulting in a massive explosion. In addition the public was told that a contract engineer working for Thiokol prepared a Failure Mode Effects Analysis (FMEA) stating that if the “O” ring were exposed to very low temperatures it would most likely fail. He presented the FMEA to his company and they in turn sent it to the NASA Manager of the solid rocket booster branch at MSFC in Huntsville, Alabama for his vetting and final approval. He in fact did sign off on everything in the FMEA including the dire prediction about the failure of the “O” ring.
Just prior to the launch an inspection team went out to check the solid motors and the composite fuel tank. The lower part of the tank contained LOX (liquid Oxygen) which is about 260-degrees below zero F. This localized cryogenic temperature and the presence of high humidity caused ice to form around the solid rocket booster. This was noted and the launch crew was notified. Members of the Thiokol management team wanted to scrub the launch in order to wait for the humidity to drop or for better conditions. NASA engineer were reluctant to scrub for two reasons, 1) they didn’t want to miss their launch window and 2)They didn’t want to upset their preplanned successive launches of the other Space Shuttles. It became a pissing contest and NASA won. The person that was most vocal on the NASA launch team was the former manager of the solid motor branch at MSFC who had signed off on the FMEA. He had been promoted and transferred to the Cape.
The rest is history. The “O” ring failed and a jet of hot gasses escaped from the defective seal.
That is what the public was told at least they were told everything except who had signed off on the FMEA and the fact he was the most vocal member of the launch team to order
the launch contrary to what the FMEA had predicted.
Now, I’ll tell you what I think happened but first, I have to talk rocket science. There are several types of solid rocket motors. The most common is that used in small missiles. These are end grain or they burn on the exposed surface. When an end grain rocket burns, it burns like a cigarette. The interior volume of the motor case determines the internal pressure of the combustion. At ignition the interior exposed volume is small so that as the propellant is ignited the pressure is quite high. But, as the propellant burns the interior volume increases and the pressure drops.
On larger solid motors the propellant grain is cast with the center of the grain constructed in a geometric shape. The shape can be in the form of a cross or possibly like a star. In this type of motor the combustion takes place on the surface of the cast in geometric shape. Contrary to the drop in pressure on an end burning propellant grain the pressure remains constant (within design parameters). If you were to measure the perimeter of the cast in geometric shape you would find it equal to the inner circumference of the containing vessel. As the grain burns away the inner exposed surfaces will become less in surface area but it is now getting close to the inner walls of the rocket motor and if all goes well the rockets will be jettisoned just before burnout.
In many large motors such as those used on the shuttle there will be large chunks blown out during the ignition sequence thus increasing the exposed area that burns. This does two things, one, it creates a combustion instability and two, it increases the internal pressure because of the increase of exposed surface available to be burned.
The same thing can happen if there is a crack in the propellant grain. That is why they X-ray the grain prior to assembling the motor. If the grain cracks the surface available to burn is increased and in turn the internal pressure in creases and can be significant enough to blow the rocket motor to hell and back.
Now, a little bit of chemistry. When you were a kid you learned about the fire triangle in that you needed fuel, oxygen and an ignition source to have combustion. Oxygen by itself does not burn and it doesn’t explode. But if you had a combustible dust in the presence of oxygen and you struck a match the explosion would be violent. That’s what happens when a grain elevator explodes.
The solid rocket motor used on the shuttle is made up of segments that are loaded one on top of the other to create the propellant grain. They strap on a pointed end at the top and at the bottom they attach a steerable nozzle. At each segment attach point they install an “O” ring to maintain the internal pressure. I had suggested to NASA that they use non-combustible putty between each segment pair to create a complete seal. As the grain burned the putty close to the burning gasses would be consumed but the primary seal would remain intact. I never heard from them and, as far as I know only the "O" ring seal area has been redesigned and they don’t use the putty.
Now we get back to the Challenger as it reaches altitude. NASA says a jet of flame and hot gasses escaped past the defective seal and impinged on the oxidizer tank causing the explosion.
If the flames hit the Oxidizer tank and caused a rupture there is no combustible material that would burn that fast as to cause the violent explosion.
You also have to ask this question. If the flame got past the seal it had to come from the internal combustion within the motor. In order to get to the seal any propellant in the area would be burning and as a result, increasing the internal pressure high enough to cause the rocket motor to explode. And, that is what I think happened.
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The Cat
[This message has been edited by Lu Zuckerman (edited 06 January 2001).]
[This message has been edited by Lu Zuckerman (edited 06 January 2001).]
To:
Regarding the Challenger explosion this is what the public was told. An “O” ring failed and allowed hot gasses and eventually a high velocity flame jet to escape past the defective “O” ring and impinge on the composite fuel and oxidizer tank resulting in a massive explosion. In addition the public was told that a contract engineer working for Thiokol prepared a Failure Mode Effects Analysis (FMEA) stating that if the “O” ring were exposed to very low temperatures it would most likely fail. He presented the FMEA to his company and they in turn sent it to the NASA Manager of the solid rocket booster branch at MSFC in Huntsville, Alabama for his vetting and final approval. He in fact did sign off on everything in the FMEA including the dire prediction about the failure of the “O” ring.
Just prior to the launch an inspection team went out to check the solid motors and the composite fuel tank. The lower part of the tank contained LOX (liquid Oxygen) which is about 260-degrees below zero F. This localized cryogenic temperature and the presence of high humidity caused ice to form around the solid rocket booster. This was noted and the launch crew was notified. Members of the Thiokol management team wanted to scrub the launch in order to wait for the humidity to drop or for better conditions. NASA engineer were reluctant to scrub for two reasons, 1) they didn’t want to miss their launch window and 2)They didn’t want to upset their preplanned successive launches of the other Space Shuttles. It became a pissing contest and NASA won. The person that was most vocal on the NASA launch team was the former manager of the solid motor branch at MSFC who had signed off on the FMEA. He had been promoted and transferred to the Cape.
The rest is history. The “O” ring failed and a jet of hot gasses escaped from the defective seal.
That is what the public was told at least they were told everything except who had signed off on the FMEA and the fact he was the most vocal member of the launch team to order
the launch contrary to what the FMEA had predicted.
Now, I’ll tell you what I think happened but first, I have to talk rocket science. There are several types of solid rocket motors. The most common is that used in small missiles. These are end grain or they burn on the exposed surface. When an end grain rocket burns, it burns like a cigarette. The interior volume of the motor case determines the internal pressure of the combustion. At ignition the interior exposed volume is small so that as the propellant is ignited the pressure is quite high. But, as the propellant burns the interior volume increases and the pressure drops.
On larger solid motors the propellant grain is cast with the center of the grain constructed in a geometric shape. The shape can be in the form of a cross or possibly like a star. In this type of motor the combustion takes place on the surface of the cast in geometric shape. Contrary to the drop in pressure on an end burning propellant grain the pressure remains constant (within design parameters). If you were to measure the perimeter of the cast in geometric shape you would find it equal to the inner circumference of the containing vessel. As the grain burns away the inner exposed surfaces will become less in surface area but it is now getting close to the inner walls of the rocket motor and if all goes well the rockets will be jettisoned just before burnout.
In many large motors such as those used on the shuttle there will be large chunks blown out during the ignition sequence thus increasing the exposed area that burns. This does two things, one, it creates a combustion instability and two, it increases the internal pressure because of the increase of exposed surface available to be burned.
The same thing can happen if there is a crack in the propellant grain. That is why they X-ray the grain prior to assembling the motor. If the grain cracks the surface available to burn is increased and in turn the internal pressure in creases and can be significant enough to blow the rocket motor to hell and back.
Now, a little bit of chemistry. When you were a kid you learned about the fire triangle in that you needed fuel, oxygen and an ignition source to have combustion. Oxygen by itself does not burn and it doesn’t explode. But if you had a combustible dust in the presence of oxygen and you struck a match the explosion would be violent. That’s what happens when a grain elevator explodes.
The solid rocket motor used on the shuttle is made up of segments that are loaded one on top of the other to create the propellant grain. They strap on a pointed end at the top and at the bottom they attach a steerable nozzle. At each segment attach point they install an “O” ring to maintain the internal pressure. I had suggested to NASA that they use non-combustible putty between each segment pair to create a complete seal. As the grain burned the putty close to the burning gasses would be consumed but the primary seal would remain intact. I never heard from them and, as far as I know only the "O" ring seal area has been redesigned and they don’t use the putty.
Now we get back to the Challenger as it reaches altitude. NASA says a jet of flame and hot gasses escaped past the defective seal and impinged on the oxidizer tank causing the explosion.
If the flames hit the Oxidizer tank and caused a rupture there is no combustible material that would burn that fast as to cause the violent explosion.
You also have to ask this question. If the flame got past the seal it had to come from the internal combustion within the motor. In order to get to the seal any propellant in the area would be burning and as a result, increasing the internal pressure high enough to cause the rocket motor to explode. And, that is what I think happened.
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The Cat
[This message has been edited by Lu Zuckerman (edited 06 January 2001).]
[This message has been edited by Lu Zuckerman (edited 06 January 2001).]
Guest
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Purple:
I'm sure Lu can tell you much more than almost anyone here about safety.
One point worth thinking about tho. If an engine fails it might not mean it simply stops developing thrust, depending on *how* it fails it could cause damage to other critical parts, eg the wing. It is arguable therefore that 2 engines are safer than 4 as there is less chance of an engine failure. I believe that Lindbergh had this in mind when he crossed the Atlantic in his *single* engined aircraft.
I'm sure Lu can tell you much more than almost anyone here about safety.
One point worth thinking about tho. If an engine fails it might not mean it simply stops developing thrust, depending on *how* it fails it could cause damage to other critical parts, eg the wing. It is arguable therefore that 2 engines are safer than 4 as there is less chance of an engine failure. I believe that Lindbergh had this in mind when he crossed the Atlantic in his *single* engined aircraft.
Guest
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To: 3 putt
You can find all kinds of information on the internet regarding the Challenger explosion but you won't find any thing about the boosters exploding as opposed to the oxidizer tank exploding.
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The Cat
[This message has been edited by Lu Zuckerman (edited 07 January 2001).]
You can find all kinds of information on the internet regarding the Challenger explosion but you won't find any thing about the boosters exploding as opposed to the oxidizer tank exploding.
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The Cat
[This message has been edited by Lu Zuckerman (edited 07 January 2001).]
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You are probably all correct about the inherent dangers of flying twins on ETOPS rules, but the most commonly used type on cross atlantic flights is the 767, and has been so for quite some time. I belive that upwards of 60 % of all transatlantic flights are performed by 2 engine jets. And even with the latest issue with CF6 engines, I cannot recall an accident with the 767 that has been attributed to ETOPS operations.
Surely, a jet engine is not 100 % failsafe, but it's damn close and that is as good as it's going to get. You are persuing a very interesting intellectual excersise.
I am not defending the calculations which says an engine won't fail for 1 10-9 or whatever, but merely that uncontained engine failures on ETOPS jets is very uncommon.
Purple Haze,
I do not, as the above should indicate, agree that transatlantic flights should be 3 or 4 engined. There are sufficient diversion options to make a 180 minute ETOPS flight perfectly safe. Sure, 3 is better than 2 and 4 is better than 3. But 2 is sufficient, so why the overkill ? It's basically about economics and passengers preferring direct flights on smaller jets over going hub to hub on 747's.
What I'm not so impressed by is Boeings ambition to obtain 207 minute ETOPS, allowing the 772LR to go trans pacific. Not because of the engines, but the lack of suitable diversions. Yes, there are airports with runways in Siberia and other exotic places, but they lack the infrastructure to support a diversion of a 300 pax jet. No shelter, no stairs, no heat, no food, no technical facilities, no nothing. But technically you can land there, and on paper that's supposedly good enough.
Comments anybody ?
Surely, a jet engine is not 100 % failsafe, but it's damn close and that is as good as it's going to get. You are persuing a very interesting intellectual excersise.
I am not defending the calculations which says an engine won't fail for 1 10-9 or whatever, but merely that uncontained engine failures on ETOPS jets is very uncommon.
Purple Haze,
I do not, as the above should indicate, agree that transatlantic flights should be 3 or 4 engined. There are sufficient diversion options to make a 180 minute ETOPS flight perfectly safe. Sure, 3 is better than 2 and 4 is better than 3. But 2 is sufficient, so why the overkill ? It's basically about economics and passengers preferring direct flights on smaller jets over going hub to hub on 747's.
What I'm not so impressed by is Boeings ambition to obtain 207 minute ETOPS, allowing the 772LR to go trans pacific. Not because of the engines, but the lack of suitable diversions. Yes, there are airports with runways in Siberia and other exotic places, but they lack the infrastructure to support a diversion of a 300 pax jet. No shelter, no stairs, no heat, no food, no technical facilities, no nothing. But technically you can land there, and on paper that's supposedly good enough.
Comments anybody ?
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To: Juliet November
The calculated failure probability of 1 10-9 is for catastrophic failure where the engine sheds some high speed rotating parts and could possibly down the aircraft or cause passenger or crew death. The actual probability of failure or reliability number for the engine is quite a bit lower that 1 10-9 probably around 1 10-6.
These failures are not for a single engine it is for all engines of that type. It doesn’t take a very long time to accumulate 1000,000 hours of total engine operating hours. Let’s say there are 1000 737s that have the same type of engine. If all 1000 aircraft flew for 2000 hours in one year you would accumulate 4,000,000 operating hours and from a statistical standpoint you would expect to have 4 engines fail for any reason that caused loss of the engine function.
The engine on the 737 has already experienced a catastrophic failure at Manchester so, from a statistical point of view you should not experience another catastrophic failure in the life of the 737.
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The Cat
The calculated failure probability of 1 10-9 is for catastrophic failure where the engine sheds some high speed rotating parts and could possibly down the aircraft or cause passenger or crew death. The actual probability of failure or reliability number for the engine is quite a bit lower that 1 10-9 probably around 1 10-6.
These failures are not for a single engine it is for all engines of that type. It doesn’t take a very long time to accumulate 1000,000 hours of total engine operating hours. Let’s say there are 1000 737s that have the same type of engine. If all 1000 aircraft flew for 2000 hours in one year you would accumulate 4,000,000 operating hours and from a statistical standpoint you would expect to have 4 engines fail for any reason that caused loss of the engine function.
The engine on the 737 has already experienced a catastrophic failure at Manchester so, from a statistical point of view you should not experience another catastrophic failure in the life of the 737.
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The Cat
