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Grunf
24th Mar 2006, 23:36
Hello all.

Before we start bashing each other as A. or B. proponents please read this carefully.
We all can not imagine what will happen with new composite structures used on A330/340, B777 and newer products (B787, A350) after 25 years.

Fatigue in composite structures is still an open issue, both in research field and in application.
In light of that, hopefully, NTSB's requirement and probably further Airbus investigative work would help.

******************************

24 MAR 2006 NTSB urges inspections of certain Airbus A.300 rudders
The NTSB urged the FAA to order inspections of the inner skin of the composite rudder surfaces of certain Airbus A-300 series airplanes. The safety recommendations (one of which is classified as urgent) address a safety issue identified during the investigation of damage found during an inspection of a rudder from a Federal Express A.300-600 airplane. The Board noted that this incident might have applicability to a more serious rudder separation that occurred last year when an Air Transat A.310 suffered an almost complete rudder separation. (NTSB)
http://www.ntsb.gov/recs/letters/2006/A06_27_28.pdf

jollyikarus
25th Mar 2006, 02:25
Hell, that's a nasty one!
And it is not only the A300 which has plastic in the tail (and elsewhere).
Hate to think about it, but there may be some gruesome times ahead...

Ikarus

Shore Guy
25th Mar 2006, 05:14
Ah, yes.......
And the high tech "tap test"......
When new materials are developed, in concert should be ways to test them. This is not the first, nor will it be the last, of recomendations/A.D.'s on composites used in primary stucture.
:confused:

arcniz
25th Mar 2006, 09:38
In the modern version of Pandora's Box, "advanced technology" is one of the trickier devils. The benefits of faster, lighter, cheaper, longer service life, etc. are tempting bait for justification of new methods and materials. Every effort is, or should be, made to ensure proper engineering and testing of the new technology, and then it goes out into the world to confront the realities of long, hard use in astonishingly difficult conditions with little tolerance for weakness and great penalties for failure.

Some technologies - such as those in engine structures and components - have maintenance intervals and teardown cycles that reveal incipient faults. Others, including primary structures and materials embedded deep within the airframe, are not amenable to casual review. Some of us speculate that the technology for evaluating the strength and margin of safety for composite materials in air carrier applications may not have caught up with the rapidly expanding use of these materials.

A similar disconnect between design element complexity and limited availability of effective means for maintenance seems likely also to become manifest in the hardware, software, and the wiring of systems for flight controls, engines, and other automated functions. A hundred years from now, perhaps very detailed and thoroughly reviewed public standards will exist for fail-soft functionality and diagnosability of all critical subsystems. At present, the standards and methods at the finest levels of detail are mostly at the discretion of the manufacturing companies, who are unlikely to freely disclose critical data about flaws when company-killing problems and litigation arise.

There will be interesting times to come, as the 21st century airframe fleet ages. A new generation of scary problems may necessitate aggressively raising the bar for maintainability methods and standards.

John Farley
25th Mar 2006, 10:44
Arcniz

Good post

It seems to me that what is happening in regard to composites being used for primary structure is that the very long final stage of development and testing is being done in service. I have no problem with that as a concept myself, even though I have no doubt that some people will die as a result. I say this because the only completely risk free way to tackle such advances is not to make them.

Whether we talk of people dying because of B737 rudder actuation or A300 rudder control forces and displacements I believe the certification authorities have got it very right when it comes to their practical approach in analysing the risks and benefits of not taking stronger retrospective modification action.

If you need to travel a long way in a short time a passenger ticket to fly somewhere is a remarkably cheap purchase that allows a very productive use of half a day. However uncomfortable, unpleasant and boring the experience may be there is no justification for suggesting it is a dangerous way to meet your objective.

Slats One
25th Mar 2006, 12:15
Is it possible to post this without being cited for anti -Airbus syndrome?
25th March 2006:NTSB cites inspections -on A300 fins- 1 being an urgent.
Got to:
http://www.ntsb.gov/letters/2006/AO6_27_28.pdf

So, away from the hype and the mass media rubbish, do we now have formal recognition of an ageing composites issue?

What of the manufacturing issues?

One thing may now be obvious, bunging the same fin design on a range of fuselages, power plants etc, with consequent effects on thrust lines, centres of pressure, polar inertia and lever arm fulcrum, never mind airflow patterns and G breaks, may be pushing the plastic too far...

airship
25th Mar 2006, 14:28
I don't understand how these "honeycomb core and fibreglass composite skin" structures can really be considered so advanced and untested :confused: ...they've been used in boat building for donkey's years now and not a single yacht I know of has ever fallen out of the sky yet! ;)

Uhmmm well, there have been a few embarassing occasions when an America's cup boat or two might have lost its keel and everyone became inverted I suppose. :uhoh:

Flight Safety
25th Mar 2006, 14:50
ASFKAP, I believe the B4 model uses an aluminum fin and rudder, but I stand to be corrected.

It seems to me that if a "tap" test (and listening to the sounds it makes) has a degree of effectness in determining if voids exist between the honeycomb inner core and outer skin of a composite structure, then this screams out to me that imaging ultra-sound methods could be the anwser for inspecting composite airframe structures.

airship
25th Mar 2006, 16:06
Delamination and blistering continue to beleaguer boat-builders well over 3 decades after composites became commonplace in the industry. And the "tap-test" is the most current form of looking for problems, provided the area is accessible to the surveyor...

This joint FAA/DoD/NASA on more modern methods of "NONDESTRUCTIVE INSPECTION OF COMPOSITES AND THEIR REPAIRS" (http://www.galaxyscientific.com/agingaircraft2002/SESSIONS/6/6B1_DHSU_DOC.PDF) might offer some insight.

Looks like FS' ultrasound technique is the way forward...

In 2012, an Air France engineer using ultrasound is inspecting a suspicious bubble in the underbelly of an A-380:

"Mon Dieu! Jacques, come and have a look at zis..."
"Sacré bleu! Eees eet what I think eet looks like?"
"Oui Jacques, she ees with child! A-320s? Twins no less!" :O

Grunf
25th Mar 2006, 22:01
Airship:
Sadly I do not see much development in that direction. Fatigue analysis is (for metals) well covered in academia. However it is still a sort of a problem in aerospace no matter how long the topic is present.
Nobody can still claim it found "the" method for crack detection, propagation etc.
Same holds for different types of composites. In my opinion, largest problem would be that different OEMs have different approach to composites in terms of application, manufacturing and after EIS keeping it functional.
It seems that every new type introduced brings new suggested repairs and inspections. It was easier with metal due to its crystal structure which was easier to predict. Still metal fatigue do present a problem, at least in aerospace.
the whole point I would like to address is that we are just getting into an era with far more composite primary structure vehicles and we can see more incidents like this simply because it is the first time we use composites in such way.
A300 is a good example because it is more or less one of the first commercial programs with composites in the structure.
Let us wait and see what will come out of more advanced programs that came out latter.

In my opinion, the only way to be sure of the flaw is to have 10exp-9 size gauges embedded all over the structure and constantly monitored. We are years away from that.

cornwallis
25th Mar 2006, 23:16
Airship, a composite yacht doesn't go from 0 to 450+ knots about six times a day, suffers a temperature change from +30 to -56c every time it flies,gets vibrated,twisted ,bent and subject to 1+g manoeuvres also a couple of times a day.
Shortly after the A330-200 was introduced Airbus had an Ad that required a large rivet job to the fin.If you are really bored and you can see them count how many rivets there are in a 330 fin.Don't forget to count both sides!I think it was around 1000+

Longtimer
26th Mar 2006, 04:17
I don't understand how these "honeycomb core and fibreglass composite skin" structures can really be considered so advanced and untested :confused: ...they've been used in boat building for donkey's years now and not a single yacht I know of has ever fallen out of the sky yet! ;)
Uhmmm well, there have been a few embarassing occasions when an America's cup boat or two might have lost its keel and everyone became inverted I suppose. :uhoh:

Of course the yachts don't use skydrol in their hydraulic systems either. Skydrol is great stuff in its place but it appears that it's place is not in the A300 tail structure.

cornwallis
26th Mar 2006, 20:23
n5296s,how do i know this? I have been flying the airbusfamily for 14 years and the physics and atmosphere have not changed!!!!

GotTheTshirt
27th Mar 2006, 07:26
Many years:} ago when metal analysis programs were still developing, we did heavy checks on aircraft that went down to the last nut and bolt.
As metalurgy developed we were able to ascertain were the critical areas were and developed electronic tequniques to inspect these areas in high definition electronically. The result was that the heavy checks were greatly reduced without impairing safety.
It seems to me that the composte aircraft has slotted into the metal aircraft maintenance program without the real handle on the long term analysis and effects.

I visited Dornier factory at Oberthingy when they were just starting the Sea star program and they told me that developing the aircraft was not the problem - developing the maintence and structural inspections were the real challange:bored:

sailing
27th Mar 2006, 07:47
Having done a bit of gliding, I'm aware that composite airframe life has become an issue as some glass gliders are over 30 years old. I believe a lot of research has been done on this, particularly by German manufacturers. Maybe a possibility to exchange information?
No bits have fallen off my (steel!) yacht lately, but then Vne is 8 knots....;)

Gauteng Pilot
28th Mar 2006, 10:37
Manufacturers always test 1 airframe to failure during certification, but I wonder what would the results be if they tested a similar one 30 years later.

Would be very interesting if manufactureres would test say a 747-200 and A300 both over 25 years old and see how they stand up compared to how the new airframes did when they were certified

JamesT73J
28th Mar 2006, 10:51
Is the vertical stab also composite on this aircraft, or is that piece aluminium? Outside of the comment about rudder failure causing a period of high loading on the fin, there isn't alot of information about this, other than a suggestion that "....high stresses may have been dangerously close in magnitude to those that caused the in-flight separation of the vertical stabiliser....involving American Airlines flight 587."

This must be an interesting area of research.

cwatters
28th Mar 2006, 11:32
Airship, a composite yacht doesn't go from 0 to 450+ knots about six times a day, suffers a temperature change from +30 to -56c every time it flies,gets vibrated,twisted ,bent and subject to 1+g manoeuvres also a couple of times a day.

Yachts get a severe pounding and they do indeed break up....

http://www.thelognewspaper.com/news/newsview.asp?c=179603

http://news.bbc.co.uk/sport1/hi/other_sports/sailing/4206497.stm

http://www.sailingbreezes.com/sailing_breezes_current/articles/July03/disaster.htm

fokker
28th Mar 2006, 11:49
Helicopters have been flying with composite blades for about 15 years now. The stresses/ 'cycles' on these must be astronomical when compared to F/Wing aircraft so they must offer a rich source of data. Has anyone done the research?

Proof Reader
28th Mar 2006, 14:55
fokker

What you say is true. However heli blades do not suffer the pressure/humidity/temperature cycles in the same way as airliners which can all affect moisture uptake. On Concorde for example there was a huge fatigue rig needed to represent the kinetic heating cycles as well as the loads.

Wino
28th Mar 2006, 15:20
Gautteng,

4 or 5 years ago boeing did just that with a a very high cycle 747. They used it to verify their ageing aircraft program. Infact parts of the aircraft can be seen in the boeing factory tour. Atleast they could a few years ago.l


Cheers
Wino

tallsandwich
28th Mar 2006, 18:57
There is not much that the marine industry can offer regarding composite knowledge. Sure, the marine sector makes good R&D contributions regarding materials and manufacturing processes but as a previous poster mentioned, this is not the challenge.

Forget anything that is done for whacky one-off racing yachts; when you are considering a product that will be used with high frequency for a long service duration, you need to look at the commercial marine sector for such products - and there is very little there that would advance the aircraft industry.

For a composite (FRP) ship or boat, the design gets certification to do a certain task for 25 years and thus remain insurable within acceptable statistical limits. The design factors used in the stress analysis are in a different league to the aircraft industry (design it then double the size in case someone drops a hammer on it). Product testing is governed by the intended loading conditions (i.e. combination of speed and sea state) and as a result almost impossible to accurately predict.

In service, the marine product gets unpredictably bashed between two fluids, one of a relatively very high density (water) and one of a very low density (air). You simply cannot take an FRP ship or boat and talk about 'loading cycles' to the structural engineers in the same way you can with a plane. The stress cycle of a boat going between two ports is not so predictable in the same way as an aircraft going between two airports.

The marine FRP inspections are relatively crude and mainly manual. Access to do this, when compared to an aircraft, is simple. Analysis result is either it (the composite) has delaminated or it has not, whether due to moisture or trauma. No one in the marine industry can tell you that this bit of composite can survive X number more loading cycles before catastrophic failure, let alone define the macro loading cycle with sufficient accuracy.

Given all the above, the marine engineering community is hardly well positioned to deliver anything of real significance.

vapilot2004
28th Mar 2006, 21:37
From the Transportation Safety Board of Canada:

"Airbus inspections of some rudders on its planes aren't frequent enough to identify problems with the aircraft"

The agency recommended more inspections after probing an incident involving an Airbus A310-300 flown by Air Transat, which lost its rudder March 6, 2005, after departing from Cuba.

The investigation "suggests that the current inspection program for Airbus composite rudders might not ensure the timely detection of defects," the Transportation Safety Board said in a statement."

This advisory comes shortly after the NTSB's urgent advisory on Friday to the FAA for an improved inspection regime for about 400 Airbus aircraft including a check for skydrol-contaminated structures.

The "urgent" recommendation by the NTSB stemmed from a Nov. 27, 2005, incident involving a rudder on an Airbus A300-600 operated by FedEx. The rudder was damaged during routine maintenance and sent to the manufacturing facility for an assessment of damage.

During the inspection, a "substantial area" of separation was found between the inner skin of the composite rudder surface and its honeycomb core, along with hydraulic fluid, which can lead to progressive separation and compromise the rudder strength, the agency said.

"Tests on the damaged rudder also revealed that disbonding damage could spread during flight," the NTSB said in a statement issued Friday.
The NTSB recommended that the FAA establish a "repetitive inspection interval" on Airbus planes without modified rudders "well below" the current standard of every 2,500 flights.


Meanwhile, Airbus denies any problems with their recommended inspection interval for these aircraft and says they will not change the maintenance schedule:

"We are still confident in our inspection schedule that we recommended to operators earlier this month," Airbus spokeswoman Mary Anne Greczyn said Monday.

"While the NTSB is recommending an expedited inspection of the relevant rudders, Airbus remains confident in the operating safety of these aircraft and our original recommendations for inspection," Greczyn said.


Later last year after the un-commanded rudder excursion was demonstrated by FedEx maintenance on one of their A300s, Airbus prudently recommended further inspections of the laminate without regulatory prodding.

I wonder why they are resisting now ?

And when will we be seeing enhanced preventative maintenance procedures on aircraft like the 777 and many others ?

turrbntrip
28th Mar 2006, 21:55
This sounds similar to the degredation of the foam core of certain types of propeller blades, when engine oil from the prop hub seeped into the area between the metal spar and the core...caused the loss of at least one Brasilia and a couple of the ATR's in our fleet were found to have weakened blades as well.

I guess petroleum products and glassfibre/composites really don't mix well after curing!

TT

arcniz
28th Mar 2006, 21:59
Given all the above, the marine engineering community is hardly well positioned to deliver anything of real significance (about strength of composites in aircraft).

Points well made, Tallsandwich.

By way of footnote, I would add:

a) With most nautical craft, excepting a few military vessels, it is relatively difficult and exceptional to be able to push them - deliberately or accidentally - up to and beyond the engineered design strength limits.

With aircraft, however, driving the airframe, engines, and systems up to and beyond design limits is possible during each and every operational use of the machine, as well as sometimes during ground handling and maintenance.

b) An important consideration relating to questions about service life of composite components vs traditional metal, wood, and other mfg techniques is that composites are typically "created" in place, with strength and durability reliant on invisible qualities derived from that creation. Like barrels of wine, each unit has some hard-to-quantify variability when made that creates unknown implications for its ultimate competence in service.

Lacking informative means to assess the future durability of composite materials incorporated in individual assembled units and units in the field, we seem to be operating in an uncomfortably dark zone of adverse possibilities. While this standard may be acceptable in military use, where composites have provided distinguished service, a much more conservative approach seems warranted in Civil Aviation, for use by the general public.

tallsandwich
29th Mar 2006, 07:52
I guess petroleum products and glassfibre/composites really don't mix well after curing!


TT - These problems can be easily overcome if they are forseen - take a look at this FRP ship - with diesel in it's FRP tanks. (http://en.wikipedia.org/wiki/Sandown_class_minesweeper)

Sure no one expects a propeller to be immersed in a hyrdocardon product as they do with a bulk fuel tank, but as a propeller blade is situated right next to a fuel tank and an engine....it could be argued that this contamination should have been forseen.

Ignition Override
30th Mar 2006, 05:47
VA Pilot 2004: You beat me to the info, at least on Pprune.

A US newspaper today published a long article on the topic and said that "FEDEX is Airbus' largest customer in the world".
What is revealing to me is that the Air Transat aircraft lost 95
% of the rudder (!) and this happened ONE YEAR AGO this month.
Is the FAA still not yet requiring US companies to make this inspection?

How much more important is the cost factor in the FAA's cost versus benefit equation?
Let's not forget the FAA's total disregard of the (documented with foreign airlines) ATR-42's unpredictable flight characteristics in certain icing conditions (aileron "snatch"), until...a smashed plane with smashed bodies in Roselawn, Indiana.

How different are the composite materials in newer Airbus A-319/320 and Boeing 787s? The problem is apparently not caused by hydraulic fluid, by itself.

vapilot2004
30th Mar 2006, 06:40
Link to NTSB urgent release regarding this:NTSB Airbus A300 Rudder (http://www.ntsb.gov/Pressrel/2006/060324.htm)

Ignition Override, you know, along with FedEx and American Airlines (the only US carriers operating this aircraft), shouldn't the remaining A300/A310 fleet be examined ?

This is not a minor issue since the A300 series has only one rudder surface. I strongly feel that Airbus needs to issue another AOT right away. The FAA is also a bit of an enigma, isn't it ?

I have an idea that the composites used in the A320 and 787 haven't changed that much since the A300 was built. Boeing claims to be using a more sophisticated monitoring system on the 787, but what about the triple 7 ?

Let us all hope that some intrepid maintenance engineers are already looking carefully at the aging composites in our collective fleets.

gwillie
1st Apr 2006, 22:48
The AD issued 30/03/06:
http://www.airweb.faa.gov/Regulatory_and_Guidance_Library/rgAD.nsf/0/20F9BF2AF4868CCD86257141005DFFDD?OpenDocument