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Old 06-05-2009, 09:08 PM
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Question Mysterious Disappearance of AF447 Baffles Experts

The latest reports on ill-fated Air France Flight 447 detail the brave efforts of its crew to regain control of the aircraft after multiple systems failures struck the doomed aircraft. Artifacts initially reported to be from the Airbus 330, with 228 aboard and presumed dead, were later found to be sea trash.

Theories abound as to why this ultramodern airliner disappeared in its otherwise routine flight from Rio De Janeiro to Paris, but experts remain deeply puzzled by its loss even as an international search continues for its so-called "black box" recorders.

What do you think happened to this flight, and how do you feel about airline safety in light of its disappearance?

My thoughts and prayers go out to those affected by this tragic loss.

Last edited by Star Trek Viewer : 06-06-2009 at 07:03 AM.
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Old 06-05-2009, 09:39 PM
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Well when you've got a storm on the flight path, any number of things can go wrong if you don't go over the storm, around the storm, or just turn back. Sadly modern does not mean failure resistant. Not by any stretch of the imagination.

Generally Airbus doesn't use a fail-safe design approach to its aircraft. It uses a safe-life approach.

Design philosophies aside, my dad is Boeing engineer of over 30 years and a was a certified pilot. The first cardinal rule he was taught about flying in the presence of a thunderstorm was, stay the f*** out of it. Multiple lightning strikes can cause major problems to your fly by wire systems. Not to mention that in an age where you're seeing more and more composites being used in aircraft, lightning strikes can really damage a structure. Lightning aside, there's also the chance of flying through hale. Perhaps whats even worse is if you're flying straight and level, and suddenly pass into an updraft of winds of say 100mph, that can rip the wings right off the plane. The thing is you can design the hell out of something but it will still have its limits. So who knows, really.
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Old 06-05-2009, 09:58 PM
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Quote:
Originally Posted by Akula2ssn View Post
Well when you've got a storm on the flight path, any number of things can go wrong if you don't go over the storm, around the storm, or just turn back. Sadly modern does not mean failure resistant. Not by any stretch of the imagination.

Generally Airbus doesn't use a fail-safe design approach to its aircraft. It uses a safe-life approach.

Design philosophies aside, my dad is Boeing engineer of over 30 years and a was a certified pilot. The first cardinal rule he was taught about flying in the presence of a thunderstorm was, stay the f*** out of it. Multiple lightning strikes can cause major problems to your fly by wire systems. Not to mention that in an age where you're seeing more and more composites being used in aircraft, lightning strikes can really damage a structure. Lightning aside, there's also the chance of flying through hale. Perhaps whats even worse is if you're flying straight and level, and suddenly pass into an updraft of winds of say 100mph, that can rip the wings right off the plane. The thing is you can design the hell out of something but it will still have its limits. So who knows, really.
Is a safe-life approach "safer" than a fail-safe approach, in your opinion, or is it the other way around? Just curious.
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Old 06-05-2009, 10:29 PM
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Is a safe-life approach "safer" than a fail-safe approach, in your opinion, or is it the other way around? Just curious.
Personally I prefer fail-safe, but safe-life can have applications.

In a safe-life design, the product is designed to survive a specific "design life" usually with a reserve built in. So typically Airbus planes are designed to function for approximately 20 years. After which the plane is to be replaced, however the drawback is that the plane could technically probably maintain service longer. The idea in a safe-life design is that a critical system is designed to work for years without the need for repairs, this is usually done in systems that are difficult to access and/or repair.

Fail-safe is a design philosophy where should a failure actually take place in a component, the system as a whole can respond in a way to minimize harm to other components or personnel. So basically if a component were to fail, that one failure should not lead to the destruction of the whole system. This is also similar to "fault-tolerant" designs.

This is why generally you don't normally see Airbus planes in service that are over 20 years old. There are probably exceptions.

In a way, I guess you could say that in safe-life, the component isn't supposed to fail in the first place. Fail-safe takes steps to be ready in case a failure does take place.

But like I said earlier, you can design the hell out of something but there are still limits to what a design can take, even one that uses a fail-safe design philosophy.
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Old 06-05-2009, 10:45 PM
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Personally I prefer fail-safe, but safe-life can have applications.

In a safe-life design, the product is designed to survive a specific "design life" usually with a reserve built in. So typically Airbus planes are designed to function for approximately 20 years. After which the plane is to be replaced, however the drawback is that the plane could technically probably maintain service longer. The idea in a safe-life design is that a critical system is designed to work for years without the need for repairs, this is usually done in systems that are difficult to access and/or repair.

Fail-safe is a design philosophy where should a failure actually take place in a component, the system as a whole can respond in a way to minimize harm to other components or personnel. So basically if a component were to fail, that one failure should not lead to the destruction of the whole system. This is also similar to "fault-tolerant" designs.

This is why generally you don't normally see Airbus planes in service that are over 20 years old. There are probably exceptions.

In a way, I guess you could say that in safe-life, the component isn't supposed to fail in the first place. Fail-safe takes steps to be ready in case a failure does take place.

But like I said earlier, you can design the hell out of something but there are still limits to what a design can take, even one that uses a fail-safe design philosophy.
Thanks for that explanation.

I think that fail-safe philosophies better take into account that one cannot really know the actual life of an individual component. For example, a widget can have a design life of 20 years, but what does that really mean? What if the widget in question has hairline cracks in it that x-ray inspections cannot catch? Then, in such a case of defect, the actual life of full reliability might only be, say, 10 years, and the last 10 years are basically unsafe-life in practice.

By comparison, in case of either a design or an individual defect, fail-safe philosophies allow for unanticipated failures such that in case of such failures, the risk to the larger system is minimized.

However, I have no independent knowledge of what Airbus's design philosophy really is, and I certainly am no expert in this area.
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Old 06-05-2009, 11:02 PM
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Yeah, safe-life is a older design philosophy. Fail safe and fault-tolerant came out as alternatives to it.

My understanding is that safe-life can work, but it's extremely tricky to do it and as you've already guessed, there is uncertainty built in. I remember one time I toured a Boeing plant and saw where they did some of their testing. One of the things that they do with some components like a landing gear is that they put it through a machine and torques it, compresses it, sheers it etc. And they keep doing that 24/7 365 days a year until it breaks. Basically what they're doing is running the component through all the stresses that it is expected to undergo during its life cycle and see how long till it fails. Do that a few times, assuming that the components are consistent in how they were made and you can get a good idea of the life cycle.

The problem however, is as my dad puts it is that your life cycle estimates are only reasonable if and only if that component during its service does not endure anything that you did not test for. So if you test say a structural beam and assumed that the plane would always steer well clear of severe storms, but during the actual service that plane has flown right through a severe thunderstorm or two then your estimate may or may not be valid anymore.
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Old 06-05-2009, 11:22 PM
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No Highway in the Sky: Starring James Stewart. Great film.

http://en.wikipedia.org/wiki/No_Highway_in_the_Sky

Never liked flying as much after I saw this movie.
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Old 06-05-2009, 11:56 PM
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This has been very interesting and has told me things about planes I didn't know before. Being a Belt and Braces kind of man, I'd favor a design that has backup systems to try and compensate for the failure of any primary system. One design philosophy seems to be built on the assumption that nothing really bad will happen to the plane, and the other on the assumption that it might.
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Old 06-06-2009, 12:35 AM
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Does the fail-safe/safe-life position relate at all to what I had read in some reports - the Airbus uses a computer control system with no mechanical back-ups? Whereas other aeroplane manufacturers do?

Either way, I'm starting to think the answer may not be known for some time, if at all. It seems that without the black box data the investigation team can't make a lot of sense of the data they do have - 'incoherent' was one word used in a press brief.

Not than I'm any kind of expert, but I think it may turn out to have been some kind of catastrophic structural failure in the middle of that storm they went through.

As for air safety - well, think of the likely number of flights that have taken off and landed without incident in the 6 days or so since the flight vanished.

As has been said - no matter how well designed a plane is, things can still go wrong to bring it down. The only reservation I would have is that if it were at all related to a design flaw, without finding the wreckage or BB, then Airbus is going to have a tough time trying to find out if they need to ground the 330 design for inspections.
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Old 06-06-2009, 05:18 AM
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Made me think of Amelia Earhart and "it looks like a lightning storm"...
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