Southwest FLT 812 Decompression and diversion
lomapaseo, I'm afraid it all starts with the insurers and actuaries. I know its a gloomy thought, but there you are.
Contrary to public perceptions, a value is put on human life. Actuaries also put assign an acceptable probability of death to any endeavour. From memory when I started my Engineering degree, the figure was about Four million to one.
Basically, what risk management is about is multiplying the probability by the cost. When you then multiply that number by the activity e.g. (million flights), you get a big number. If you can then take some safety action that reduces the probability of a given accident, you can then quantify what the savings will be in the long term, if the cost of taking action is less than the savings you are in the money and you take the safety action.
This concept of "affordable safety" underpins all engineering. This is why your aircraft does have non inflammable furnishing materials but doesn't have individual parachute equipped escape pods.
Contrary to public perceptions, a value is put on human life. Actuaries also put assign an acceptable probability of death to any endeavour. From memory when I started my Engineering degree, the figure was about Four million to one.
Basically, what risk management is about is multiplying the probability by the cost. When you then multiply that number by the activity e.g. (million flights), you get a big number. If you can then take some safety action that reduces the probability of a given accident, you can then quantify what the savings will be in the long term, if the cost of taking action is less than the savings you are in the money and you take the safety action.
This concept of "affordable safety" underpins all engineering. This is why your aircraft does have non inflammable furnishing materials but doesn't have individual parachute equipped escape pods.
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the stress history determines when the component will fracture
For other componens (e.g. wing lower skin) a lot of statistics is needed to define the life of the component.
Volume:
Agree 100%. As for wings, I assume these days what with data storage, miniature accelerometers, etc. it is possible to integrate strain (or an analogue of strain) with respect to time and store the results, thus being able to distinguish between aircraft with different duty cycles and environments.
I think engine rpm and T's and P's are already recorded for disk life limit calculations, but I'm getting out of my depth here.
True statement. However, as the longitudinal lap joint is mainly loaded by cabin pressure and cabin pressure (hence stress levels) are closely controlled by a dedicated system, stress history for this component is almost 100% determined by flight cycles.
For other componens (e.g. wing lower skin) a lot of statistics is needed to define the life of the component.
For other componens (e.g. wing lower skin) a lot of statistics is needed to define the life of the component.
I think engine rpm and T's and P's are already recorded for disk life limit calculations, but I'm getting out of my depth here.
I think engine rpm and T's and P's are already recorded for disk life limit calculations, but I'm getting out of my depth here. I Agree 100%. As for wings, I assume these days what with data storage, miniature accelerometers, etc. it is possible to integrate strain (or an analogue of strain) with respect to time and store the results, thus being able to distinguish between aircraft with different duty cycles and environments.
Nobody's got the time to records and calculate the infinite variations in duty cycles and stress.
The cyclic life is typically predicated on a statistical stress level and duty cycle. Sometimes even an overstress condition (above the typical stress) can lengthen the cycle life considerably. confusing isn't it???
sorry about the rambling ... but its cocktail time here and I'm feeling it
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Or can gauge what idiot is going to use an unapproved scrapper/knife on a lap joint.. or the unscruplous inspector that pens it off without carrying out the prescribed measurement / correct rectification..
Wouldn't surprise me if a scribe line was the stress raiser that induced this skin failure.
Wouldn't surprise me if a scribe line was the stress raiser that induced this skin failure.
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stress history for this component is almost 100% determined by flight cycles.
If the aircraft routinely 'cycles' between low and high alt conditions, the model busts.
Another missed component is with the aircraft parked in the southwest, power off for months, cycling cold, condensation, hot weather conditions.
Don't confuse testing with the assesment of probability and severity of failures.
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Reality changes your factors and the variable factor of events we can not predict is reality.
The problem when dealing with extremely long odds is that we never can tell what happened, in reality. If I tell you the odds of getting hit by a car crossing the road are a trillion to one and tomorrow you go out and get hit by a car crossing the road, what just happened? Were you just amazingly unlucky? Was my probability calculation wrong? It's impossible to say with certainty.
If the odds of an airliner spontaneously combusting inflight is a trillion trillion to one it's still remains a possibility that you and I could see three of them do it tomorrow. If time is infinite, then anything whose odds of occurring is less than infinite will happen sooner or later.
Personally, I don't think that either the FAA or Boeing knows what just happened in reality. Nor do they care. They are politicians and businessmen and not metaphysical philosophers. They just want to cover their ass and make sure they have someone to blame reality on, whatever it is.
Mountainbear:
It isn't as bad as that. There is a small element of backside covering, but the reality is that if people perceive air travel to be unsafe, then they aren't going to use it. Bear in mind that before stratospheric jet travel was available, air travel was a lot more dangerous than it is today.
What we strive for is reliability what that means is that the bits that make up an airliner perform consistently exactly the same way all the time. It matters not how long they last, although the bean counters care about that, what matters is that they all behave predictably.
You are right to a point when you say that we cannot predict "reality" for an individual aircraft. We don't even try as far as i know.
However what we actually do is some what different; what we say is as follows:
For critical components whose failure is catastrophic; "based on our experience with thousands of aircraft flying for Tens of thousands of hours and landings and takeoffs, we are 99.999 percent sure that such and such a component is going to last at least this long" before we change it. (hard time)
For components that we have designed to be fail safe or damage tolerant, like the skin of the aircraft in question; "based on tests and long experience of failures, if this part fails we will know about it because it will announce itself in plenty of time for us to land and take corrective action". (on condition)
For components that wear out; "we will measure this, and if it is worn out we will replace it before it causes harm." (condition monitored)
For components that don't have any effect on airworthiness - seat jacks, interior lights and in flight entertainment systems they are "as required".
Don't nit pick, it's a simplified description.
Personally, I don't think that either the FAA or Boeing knows what just happened in reality. Nor do they care. They are politicians and businessmen and not metaphysical philosophers. They just want to cover their ass and make sure they have someone to blame reality on, whatever it is.
What we strive for is reliability what that means is that the bits that make up an airliner perform consistently exactly the same way all the time. It matters not how long they last, although the bean counters care about that, what matters is that they all behave predictably.
You are right to a point when you say that we cannot predict "reality" for an individual aircraft. We don't even try as far as i know.
However what we actually do is some what different; what we say is as follows:
For critical components whose failure is catastrophic; "based on our experience with thousands of aircraft flying for Tens of thousands of hours and landings and takeoffs, we are 99.999 percent sure that such and such a component is going to last at least this long" before we change it. (hard time)
For components that we have designed to be fail safe or damage tolerant, like the skin of the aircraft in question; "based on tests and long experience of failures, if this part fails we will know about it because it will announce itself in plenty of time for us to land and take corrective action". (on condition)
For components that wear out; "we will measure this, and if it is worn out we will replace it before it causes harm." (condition monitored)
For components that don't have any effect on airworthiness - seat jacks, interior lights and in flight entertainment systems they are "as required".
Don't nit pick, it's a simplified description.
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I am surprised no one today has picked up on what was said yesterday,
This is a passage from flightglobal
Speaking at the MRO Americas conference in Miami, FAA administrator Randy Babbitt said: "People have leaped to the conclusion that it was fatigue. The airplane didn't have that many cycles on it so we're looking at other things. The manufacturing techniques. Boeing is very interested too. This is not good for anybody's business."
This is a passage from flightglobal
Speaking at the MRO Americas conference in Miami, FAA administrator Randy Babbitt said: "People have leaped to the conclusion that it was fatigue. The airplane didn't have that many cycles on it so we're looking at other things. The manufacturing techniques. Boeing is very interested too. This is not good for anybody's business."
Shell Management:
If you don't think risk management is about money, then you are deluded. I never said that insurance is a mitigator, what I said was that insurance requirements ultimately drive risk management programs.
To put it another way; Insurers will make you do these things, or no insurance at any price.
Why do you think the technical and standards arms of Lloyds, Det Norsk Veritas, etc. exist otherwise?
Clearly if you were taught by Exxon and think that risk management is about insurance you had a poor teacher who doesn't under stand the concept (or you have the IQ of a hermit crab). Insurance is one mitigation but not a very effective one. I suggest you read this:
To put it another way; Insurers will make you do these things, or no insurance at any price.
Why do you think the technical and standards arms of Lloyds, Det Norsk Veritas, etc. exist otherwise?
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22 years ago when my base became a 737 base and I stopped flying the lovely DC9 (Thank God mind you, how many jobs I have had subsequently thanks to that rating) I remember feeling a bit underwhelmed by the perceived "quality" of my new steed.
I remember being horrified at what I was looking at whilst performing external inspections/walk-rounds . . . whatever we call it these days.
"For christs sake" I used to muse," do Boeing make aircraft or ships ?"
Don't know if the worst was the "slap it together with rivets and never mind the overlapping joints" or the " orange peel is not only for middle aged womens legs , it is fine for lower aft fuselage panels" that bothered me the most.
If you were used to the smooth flawless surface, that one rather expected on a high speed vessel & certainly found on a DC9 , the 737 was a bit of an eye opener.
Maybe my initial impressions were right . . . quality product ? ? well, maybe not, but has the "quality" been enough, that may prove to be THE question.
I remember being horrified at what I was looking at whilst performing external inspections/walk-rounds . . . whatever we call it these days.
"For christs sake" I used to muse," do Boeing make aircraft or ships ?"
Don't know if the worst was the "slap it together with rivets and never mind the overlapping joints" or the " orange peel is not only for middle aged womens legs , it is fine for lower aft fuselage panels" that bothered me the most.
If you were used to the smooth flawless surface, that one rather expected on a high speed vessel & certainly found on a DC9 , the 737 was a bit of an eye opener.
Maybe my initial impressions were right . . . quality product ? ? well, maybe not, but has the "quality" been enough, that may prove to be THE question.
If you don't think risk management is about money, then you are deluded. I never said that insurance is a mitigator, what I said was that insurance requirements ultimately drive risk management programs.
To put it another way; Insurers will make you do these things, or no insurance at any price.
Why do you think the technical and standards arms of Lloyds, Det Norsk Veritas, etc. exist otherwise?
To put it another way; Insurers will make you do these things, or no insurance at any price.
Why do you think the technical and standards arms of Lloyds, Det Norsk Veritas, etc. exist otherwise?
In all my dealings with the consortiums, they simply conducted audits against my process and compared it to their overall risk. I then justified my on-the-job performance against the relative cost of this insurance to my own (secret) standard.
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I wish to echo captainplaystation's feelings on the difference between the DC9 and the 737.
First, one must understand that these two planes were built (original versions) around the same time, to do the same job.
The Douglas design is simply more robust in structure and its systems are the definition of KISS (keep it simple, stupid)..
Given a choice, if someone were to offer me a thirty year old DC9-30, a brand new 737ng, or a brand new Airbus 320 series, I would take the DC9 if it was properly maintained .
And I would bet that in 20 years, the other two planes would have been retired and my 9 would be fine.
First, one must understand that these two planes were built (original versions) around the same time, to do the same job.
The Douglas design is simply more robust in structure and its systems are the definition of KISS (keep it simple, stupid)..
Given a choice, if someone were to offer me a thirty year old DC9-30, a brand new 737ng, or a brand new Airbus 320 series, I would take the DC9 if it was properly maintained .
And I would bet that in 20 years, the other two planes would have been retired and my 9 would be fine.
[The Douglas design is simply more robust in structure]
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Haven't read the entire thread...so it might have already been said....but I agree with the couple posts about the 9....completely different philosophy on aircraft design...
Main problem is...each airline deals with aircraft "fatigue" in different ways...depends on the airlines "authority" and "recommended" practices from the manufacturer.....This is a slippery slope.
Airline A could check the structural integrity of the 737 every 5000 hours and Airline B could do the same check every 20,000 hours and it's all legal....
It's only when the sunroof occurs....that the "authority" decides that we must look into the fatigue issue....
As far as I know....Southwest with about 80 aircraft and Alaska with about 2 where the only two airlines in the USA that needed to have their aircraft inspected and were grounded till inspected....I could be wrong, but that is what I have read...
That being said, what else is Southwest or Alaska not doing that the other airlines in the USA or Worldwide are?? Not pointing fingers, and not saying they did anything illegal....I do not think they did anything wrong, they just went by Boeing and their FSDO's rules...
So the question is....what happens with the rest of the operators of the 737's around the world???
Last, I miss the Douglas products.....what great machines!!!!
Main problem is...each airline deals with aircraft "fatigue" in different ways...depends on the airlines "authority" and "recommended" practices from the manufacturer.....This is a slippery slope.
Airline A could check the structural integrity of the 737 every 5000 hours and Airline B could do the same check every 20,000 hours and it's all legal....
It's only when the sunroof occurs....that the "authority" decides that we must look into the fatigue issue....
As far as I know....Southwest with about 80 aircraft and Alaska with about 2 where the only two airlines in the USA that needed to have their aircraft inspected and were grounded till inspected....I could be wrong, but that is what I have read...
That being said, what else is Southwest or Alaska not doing that the other airlines in the USA or Worldwide are?? Not pointing fingers, and not saying they did anything illegal....I do not think they did anything wrong, they just went by Boeing and their FSDO's rules...
So the question is....what happens with the rest of the operators of the 737's around the world???
Last, I miss the Douglas products.....what great machines!!!!
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Shell,
I understand that and I never said that either SWA or Alaska did not use Boeings guidance.
I said other airlines in the USA must have gone above and beyond the guidance that both SWA and Alaska had been following for those particular airframes. Not trying to pick on either airline, they did nothing wrong. But, USAir and United which both have some older 300's of the same era did not have any issues after inspections were complete. (that I know of anyway)
The real issue is....when these older 300's find there way to a foreign nation, who's guidance will they be using??
I understand that and I never said that either SWA or Alaska did not use Boeings guidance.
I said other airlines in the USA must have gone above and beyond the guidance that both SWA and Alaska had been following for those particular airframes. Not trying to pick on either airline, they did nothing wrong. But, USAir and United which both have some older 300's of the same era did not have any issues after inspections were complete. (that I know of anyway)
The real issue is....when these older 300's find there way to a foreign nation, who's guidance will they be using??