noistar
Final Assembly Line stage 2
Posts: 388
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Post by noistar on Jan 22, 2014 19:49:34 GMT 1
Thought I'd already posted this
Perhaps I'm idealistic and certainly naive when it comes to my opinions on safety procedures for the certification of modern new aircraft designs.
I'm whiling away the time on the haul from BKK to LHR (finally on an A340 with lightweight cabin crew!)
The flight stats continually show in-flight outside temperatures of between -50 and -62C. This is for the best part of 13 hours. The plane leaves the heat of Bangkok where it's been sitting (standing?) for nearly 24 hours and climbs into the frozen flight regime. A scenario which is hardly unique.
My comments re why the A380 fatigue frame didn't pick up the flaw in the wing design(?) manufacture(?) were dismissed on the forum as it's not practical to test everything.
Why not?
If an actual flight cycle includes flying at 35,000ft in very sub-zero temperatures, after a transition from 40C, I would expect a frame dedicated to simulating those cycles to take that into account. Practicalities/costs aside, what is the point of performing fatigue tests which fail to pick up faults which occur due to fatigue?
The thousands of flight cycles which MSN5001 performed - "more than a production frame would perform in an average life time" - appear to have been, at least to a degree, a waste of time and effort.
Did the fatigue wings display the production wing flaw? If they did, the frame performed its role, in which case was it missed during the tests - a more acceptable 'failure' ie human error which can be taken into account in the future.
If they didn't, WHY NOT?
I remain convinced that Certification Agencies must become more pro-active and aggressive towards the new procedures being introduced in the name of economy/efficiency.
I don't know if it's a reasonable assumption that previously Boeing and Airbus have been left to their own devices, doing the same types of test for every new design - Serial 1 does this, Serial 2 does this, Serial 3 does this, etc etc. Serial 1, 'tick', Serial 2, 'tick'. (Perhaps we ought to add 'Fatigue Frame 'tick').
While it's obvious that manufacturers don't deliberately generate unsafe designs, the watchful eye of organizations who only think SAFETY, not predominately MONEY, is surely the way forward. There will always be compromises, but at least they should be well thought out.
The agencies would need to be able to stand up to the big boys who presumably have a lot of influence.
If a B787 is lost due to a battery, ie design fault, who is to blame, the manufacturer or the Agency(ies) which Certified the design as safe? Cold comfort for the relatives of casualties I know.
No test regime will ever be perfect - the RR engine 'failure' occurred after very demanding tests after all.
Sorry to ramble on, especially as I am not an aviation professional and therefore can only base my comments on assumptions and, I hope, common sense.
BTW, I seem to recall an EC135 derivative being lost in unexplained circumstances. One of the theories was that the composite (I believe) replacement frame section failed. The composite section was intended to allow electronic surveillance hardware to work free of the interference of the metal original. A new design feature which was possibly assumed to be acceptable.
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philidor
in service - 6 years
Posts: 8,950
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Post by philidor on Jan 22, 2014 22:04:02 GMT 1
Metal fatigue played no part in the A380 wing crack issue, so it is not surprising that they could not be predicted by fatigue tests. This was shown by the fact that all frames - whether they were brand new or had been in service for years - were prone to cracks.
A double cause was eventually identified : a faulty design of some small parts of the wing + a manufacturing practice introducing excessive stress during the building process. That is why Airbus closed its wing factory for some time (to implement process changes) and introduced a new design.
Actually, these cracks were never close to becoming a safety issue.
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noistar
Final Assembly Line stage 2
Posts: 388
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Post by noistar on Jan 23, 2014 7:50:13 GMT 1
Metal fatigue played no part in the A380 wing crack issue, so it is not surprising that they could not be predicted by fatigue tests. This was shown by the fact that all frames - whether they were brand new or had been in service for years - were prone to cracks. A double cause was eventually identified : a faulty design of some small parts of the wing + a manufacturing practice introducing excessive stress during the building process. That is why Airbus closed its wing factory for some time (to implement process changes) and introduced a new design. Actually, these cracks were never close to becoming a safety issue. I'm sorry if my post gave the impression that the wing issue on the A380 was a safety issue - I acknowledge the fact it wasn't. However, my point stands, the fatigue frame sitting in its nice house, being put through cycles, is not doing what it claims 'on the tin'. It is performing a very limited cycle, which does not represent the life of a frame. In fact, I imagine it's very difficult to perform a simulation due to the time factor. How long does it take for a frame to warm up, cool down, in its flight? I remain to be convinced that the fatigue frame is actually representative of anything. A plane takes off, has stresses applied in its bubble of ground level environment, and lands again. I apologise for not having solutions to offer, clearly due to my lack of qualification in the discipline. I believe the fatigue frame tests take-offs and landings and how the frame supports itself in flight, for a 'lifetime', albeit in a non-representative regime. I don't believe it is representative of a lifetime of 'work'. Presumably it is not Airbus' intention to claim it is, but it does make me wonder what customers and certification agencies believe the benefit is. I would like the discussion to move on from one-line dismissals/ defenses of my points and into my intention to debate whether design has reached a new level, where technology is being pushed near to its limit in the name of, money. Is the design/manufacture/test environment the same as it always was or should the safety agencies be becoming more pro-active? I imagine things are different due to the continual list of changes - of 'new' materials, techniques, hardware etc. i do not have a down on the B787 - both the B787 and A350 are prime examples of the new regime. The B787 is in the frame because it 'is', the A350 because it 'will be'. The B787 may be a new 'electric' design, which should have been tested as such. Is there an opinion to my question about who has responsibility for the loss of a B787 due to, or contributed to, a battery fire - Boeing or the certification agencies? Hopefully my posts on many threads show my thirst for information. The forum is full of professionally qualified members who can pass on their knowledge and opinion to the forum in general. Don't shoot the messenger - my questions are intended to stimulate debate, or at least a contribution to the whole issue. Cherry picking my posts is not my intention  |
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philidor
in service - 6 years
Posts: 8,950
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Post by philidor on Jan 23, 2014 10:34:58 GMT 1
Security requirements are steadily increasing, or adapting to a changing industry environment, but regulations remain a trade-off between security concerns on the one hand, what the aircraft manufacturing industry can deliver and what airlines actually can implement on the other hand.
ETOPS rules, which determine how far (in terms of flight hours) from the nearest diversion airport a twin-jet airliner is allowed to fly, are a perfect exemple. The maximum number has been progressively increased to acknowledge engine reliability improvements. The rule now allows up to 330 minutes ('ETOPS 330'), subject to certain conditions, and Airbus is said to apply for 'ETOPS 420' at some stage after A350 introduction.
That relaxation of safety rules has caused no catastrophe so far, in part because engines actually are reliable, and because few airlines make use of the full scope of ETOPS rules. If however such a terrible event happened, we would all have some soul-searching to make, and the first question certainly would be 'why did it take a catastrophe to make people become conscious of that impending risk ?' Nobody however is proposing a come-back to stricter rules ...
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bvb09
Final Assembly Line stage 1
Posts: 208
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Post by bvb09 on Jan 23, 2014 11:08:34 GMT 1
Sorry for my persistence, as I already asked about this in the thread Airbus A350 - General Discussion (2014) :
Does anyone know how the mentioned flight hours from the nearest diversion airport are actually determined as the calculation has to take into account that the aircraft would run on just one engine? How fast would "single engined speed" be compared to regular (i.e. double engined) speed?
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philidor
in service - 6 years
Posts: 8,950
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Post by philidor on Jan 23, 2014 11:53:05 GMT 1
Sorry for my persistence, as I already asked about this in the thread Airbus A350 - General Discussion (2014) :
Does anyone know how the mentioned flight hours from the nearest diversion airport are actually determined as the calculation has to take into account that the aircraft would run on just one engine? How fast would "single engined speed" be compared to regular (i.e. double engined) speed?
Nothing wrong with insisting, but this is a very pointed question. I personnally have no idea of the details (do you take wind conditions into account ... ?). I hope somebody else on this forum has, but I am not so sure ! |
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noistar
Final Assembly Line stage 2
Posts: 388
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Post by noistar on Jan 23, 2014 13:19:19 GMT 1
Security requirements are steadily increasing, or adapting to a changing industry environment, but regulations remain a trade-off between security concerns on the one hand, what the aircraft manufacturing industry can deliver and what airlines actually can implement on the other hand. ETOPS rules, which determine how far (in terms of flight hours) from the nearest diversion airport a twin-jet airliner is allowed to fly, are a perfect exemple. The maximum number has been progressively increased to acknowledge engine reliability improvements. The rule now allows up to 330 minutes ('ETOPS 330'), subject to certain conditions, and Airbus is said to apply for 'ETOPS 420' at some stage after A350 introduction. That relaxation of safety rules has caused no catastrophe so far, in part because engines actually are reliable, and because few airlines make use of the full scope of ETOPS rules. If however such a terrible event happened, we would all have some soul-searching to make, and the first question certainly would be 'why did it take a catastrophe to make people become conscious of that impending risk ?' Nobody however is proposing a come-back to stricter rules ... Is the Qantas engine incident worth bearing in mind when stating 'engines are reliable' and that 'relaxation of safety rules has caused no catastrophe yet'. Seems I'm on a one man crusade when it comes to suggesting that effort should be made in ensuring designs are as safe as they can be. Complacency rules. Seems that any suggestion of change results in a Luddite response of 'why change, it's been ok so far'. |
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bvb09
Final Assembly Line stage 1
Posts: 208
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Post by bvb09 on Jan 23, 2014 14:07:48 GMT 1
Sorry for my persistence, as I already asked about this in the thread Airbus A350 - General Discussion (2014) :
Does anyone know how the mentioned flight hours from the nearest diversion airport are actually determined as the calculation has to take into account that the aircraft would run on just one engine? How fast would "single engined speed" be compared to regular (i.e. double engined) speed? Nothing wrong with insisting, but this is a very pointed question. I personnally have no idea of the details (do you take wind conditions into account ... ?). I hope somebody else on this forum has, but I am not so sure ! Well, I searched the Internet before I first asked, but for example the article "ETOPS" in english Wikipedia didn't help a lot. So now I tried german Wikipedia (which in many cases is much less detailed than the english Version) and found the following: "Die tatsächliche maximale Entfernung zu einem Ausweichflughafen errechnet sich ... indem pro 60 „ETOPS-Minuten“ 400 Nautische Meilen zugrundegelegt werden... In Grenzfällen akzeptiert das Luftfahrtbundesamt 405 NM." This basically means that the actual distance to a diversion airport is calculated based on equating 60 ETOPS-minutes with 400NM. In borderline cases the Luftfahrtbundesamt (the national civil aviation authority of Germany) would also accept 405NM. An Airbus press release related to the A330's ETOPS certification even correlates 240 minutes with 1700NM, so that would be a single-engined speed of 425kts/h. I'm not quite sure about the relevance of the Luftfahrtbundesamt in the certification process, but I am quite surprised that today's twinjet aircraft seem to be able to cruise at about 80% of their regular Speed for several hours on just one engine.
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philidor
in service - 6 years
Posts: 8,950
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Post by philidor on Jan 23, 2014 14:40:50 GMT 1
Sorry, noistar, the following reply is probably one more instance of what you call a "Luddite response".
The Qantas A380 engine issue was NOT a design issue, it was a quality control issue at Rolls-Royce. It was determined that the metal used to manufacture some parts of the defaulting engine was sub-par and not on design. Rolls-Royce took full responsibility, and no engine design change was implemented as a consequence of that event (which however allowed the discovery of wing-cracks).
If you want to pinpoint major safety issues, I suggest that you turn some of your attention to crew training and management, and to quality control. I believe nowadays indequate training and excessive workloads (a true "safety vs profit" matter) are more important safety issues than design - which does not mean the only ones. As for quality control, I suppose it is increasingly difficult in the modern context of complex international supply chains (as you probably know, all kinds of unapproved cheap parts find their way into aircraft).
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noistar
Final Assembly Line stage 2
Posts: 388
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Post by noistar on Mar 17, 2014 19:31:14 GMT 1
Sorry, noistar, the following reply is probably one more instance of what you call a "Luddite response". The Qantas A380 engine issue was NOT a design issue, it was a quality control issue at Rolls-Royce. It was determined that the metal used to manufacture some parts of the defaulting engine was sub-par and not on design. Rolls-Royce took full responsibility, and no engine design change was implemented as a consequence of that event (which however allowed the discovery of wing-cracks). If you want to pinpoint major safety issues, I suggest that you turn some of your attention to crew training and management, and to quality control. I believe nowadays indequate training and excessive workloads (a true "safety vs profit" matter) are more important safety issues than design - which does not mean the only ones. As for quality control, I suppose it is increasingly difficult in the modern context of complex international supply chains (as you probably know, all kinds of unapproved cheap parts find their way into aircraft). The point of my original post appears to have been lost in the name of this thread. My concerns related to the modern methods of aircraft construction. To save a bit of weight, to improve fuel consumption, is bringing in new materials and production techniques. The 787 issue IS a design issue. As I've pointed out, it is known and has been known for a long time that these batteries present a hazard in a flying environment. So, why did Boeing and Airbus think it was safe? Thankfully we haven't got an air crash investigation asking these questions. To dismiss the failure of these changes as 'well the regulators can't know everything' is an unbelievable statement. While I'm sure(!) a well trained flight crew can fly a plane which is burning around them, my original point remains - if planes are built differently, somebody needs to challenge the products which the designers come up with. |
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