Daniel Larusso

Why are composites crazy and unsafe anytime that they are on Airbus aircraft, and creative and revolutionary when used on the 787?

jetblaster

Composites are here to stay, no doubt.

But, in answer to Daniel's question, and to comment on Bravo64: Airbus still contends that exterior visual inspection methods with the naked eye, coupled with the old "coin tap test" is adequate to find hidden damage, fatigue or delam in both monolithic carbon fiber composite construction (like the A300 tail lugs) or the honeycomb nomex matrix composite used in rudders and elevators.

Look closely at the wing failure numbers on the A380--they weren't building the airplane to pass the minimal ultimate load threshold by a good margin...they were trying to hit it exactly. This is a change in philosophy--ultimate load was never supposed to be "the target"...

...but cutting corners is what Airbus is all about and there are at least 265 fatalities in a smoking hole in Long Island that show what happens when you cut corners to get an edge on Boeing. As for design, look at the tail of the 777--it is composite, but it is constructed much differently than the A300/A320/A330/A340 tails, with dozens of attachment points that avoid metal-to-composite stress/friction points and there are titanium piers that insure that, if the vertical fin does break off, at least a stub will be left.

That's why, Daniel...Boeing does it better, safer and stronger--they recognize the FAA/JAA certification "standards" to be the "sub-standards" they really are.

Bravo64--do you have a link for the re-certification of the tail? They "beefed" it up, did they? Did they re-certify it with another test, or just "call it good."

(I have much less confidence in the FAA than you do...just look at the 737 rudder issue for a glimpse at their track record.)

Jetblaster

rickair7777

Following the AA crash, AW&ST asked Boeing and Airbus about their respective approaches to the FAA's minimum design criteria for transport vertical stabs. This criteria basically says it's OK if the rudder and/or vertical stab fall of after being cycled full-scale more than once.

Boeing stated that the FAA design spec was ludicrous, and that boeing over-engineered the vertical stuff by a massive factor.

Airbus, when asked the same question..."No Comment"

luv2fly

Boeing also runs a small wire through their composite structures so the integrety can be checked by running a current through them.

bravo24

I don't have a link for recertification of the tail - I was referring to the wing ultimate load test. I've been told by some structures engineers at a A380 customer airline that Airbus made some changes to the wing and the EASA bought it off through a paper analysis so Airbus didn't have to break another wing. My guess is that they were close enough so that relatively minor changes (i.e. thicker wing skins and/or beefed up spars) fixed the problem. I'm just curious about what they plan to do to the airplanes that were built before the changes were incorporated. And just about any improvements that make will add more weight to an already obese airplane.

Complying with the 1.5 ultimate load requirement can be a two-edged sword. Since the 1.5 number is a certification requirement, falling short is not an option. Exceeding the requirement, which most pilots may regard as a good thing, usually means more weight which means more money. It gets to be a matter of how far the manufacturer and the airline wants to go.

And if it will make any of you feel better the technology of testing composites have moved far beyond the old quarter tap test. There are a lot of new testing techniques out there (digital radiography, shearography, microwaves, and thermography for example) that do an excellent job of detecting potential problems. This is a big improvement over aluminum where the first indication of a problem is often either a crack or corrosion.

B757200ER

I think the A380 is a hunk of junk. They'll never reach the break-even point on sales.

jetblaster

Not true, at least, not true according to the latest
NTSB Safety Recommendation and AOT issued by Airbus in response to the Air Transat and Fed Ex tail/rudder disintegrations. They STILL advocate that the visual and coin tap is "good enough"...at least for the A300 and A310. That is what is so shocking...that Airbus can lose essentially four tails in a row on that aircraft type, yet still stand by the coin tap and visual test. (See the NTSB website if you wish to read the entire document, it was the Safety Recommendation that came out in May of 2006 on the Airbus 300/310).

The fact that a knowledgeable person like yourself seems to think otherwise is part of the problem...

**we assume** that the newest technology is being used...but, in fact, **it is not in all cases.** The A300 and A310 is a glaring case.

As far as aluminum goes, the eddy current electrical testing--a form of NDT--was instituted after the Ahola "convertable" room peel back on their 737, found to be corrosion and fatigue.

And, a "paper fix" on the A380 wing is what I was afraid of...and I share your concern on the pre-existing wings. Finally, more weight is part of the safety margin that Boeing has been willing--and is still willing--to "suffer" to make sure their aircraft don't fall apart in midair, like AA 587, AA903, Air Transat 961, etc.

Jetblaster

bravo24

First of all, I don't think that I stated in my post that I believe that tap tests and visual inspections are "good enough" to determine the structural integrity of composites. If that is what came across, it wan't my intent. The point I was trying to make is that NDT techniques for composites has made significant advances since the early days.

Aircraft maintainers have several different options available to them when it comes to inspecting composites or any other material used on an airplane. Which of these tools is used depends on the situation (i.e. ramp or hangar), the type of material, the type of structure, and the maintenance procedure. There are no silver bullets and no single test is the optimum choice for all situations. While you seem to have a problem with visual inspection, that is probably the most important and most useful method available. After all, isn't that what a walk-around inspection is?

The tap test used to be the primary means of testing composite structure. While there have been several new and more accurate NDT methods (such as I listed earlier) to determine the structural integrity, the tap test is still considered a valid means to discover certain types of of flaws in composites. Often when a component fails a tap test the next step is to follow up with a more comprehensive (and complex) test.

And while you are right about eddy current testing being a way of testing aluminum structure, it is usually only when specifically mandated by either a maintenance task card, AD, service bulletin, or by engineering. Most structural discrepancies are discovered by the old Mk II eyball.

jetblaster

No, I didn't think you advocated them; but the fact is, Airbus STILL insists that tap test or visual is all that is needed in the testing of A300 or A310 composite components, despite the clear failures of such methods on AA 903, Air Transat 961 and the Fed Ex jet from Nov 2005.

>>>>Aircraft maintainers have several different options available to them when it comes to inspecting composites or any other material used on an airplane. Which of these tools is used depends on the situation (i.e. ramp or hangar), the type of material, the type of structure, and the maintenance procedure.<<<

And my point remains that Airbus DIRECTS operators to ONLY use tap tests and visual inspections to find even suspected problem areas of delamination. Look at the last three AOTs issued by Airbus in regard to A300 or A310 rudders. These were issued over the last five years. None of them found the damage that was discovered on Fed Ex tail in Nov 2005; in fact, even after a mistake damaged a rudder in the hangar and they saw the previously-undiscovered delam, they conducted tap testing and found only a limited area of delam; but, thinking with their heads, they also conducted ultrasonic NDI and found a much larger, more critical delam that was not found using the inspection methods that Airbus advocated. Read all about it in the March 2006 Safety rec from NTSB.

Here is a quote from a letter written by some A300 pilots at AA to the NTSB shortly after that Safety Rec:

On March 24, 2006, the NTSB issued a Safety Recommendation that urged the FAA to, among other things, require inspections of A-300/A-310 rudders immediately, dramatically rejecting an Airbus All Operators Telex (AOT) that instead called for an inspection exemption for some A-300/A-310 aircraft and an extended period of flight on the rest of the aircraft prior to inspection or delay in repair after discovery of damage. This recommendation was remarkable because it told of delamination that had occurred on a FedEx A300 rudder, discovered when damaged in a hangar test. The discovery was significant because, according to the NTSB, it implicated intrusion into the composite material composing the rudder by hydraulic fluid as a cause for “propagation” of the delamination, and that the normal inspection methods used to insure composite integrity would not have discovered this damage:

Further examination of the disbonded area revealed traces of hydraulic fluid. Hydraulic fluid contamination between the honeycomb skin and the fiberglass composite skin can lead to progressive disbonding, which compromises the strength of the rudder. Tests on the damaged rudder also revealed that disbonding damage could spread during flight.

The investigation found that the areas specified in the AOT did not include the areas in which the disbonds were found on the incident rudder. Further, it was determined that tap tests on the external surfaces of the rudder likely would not have disclosed the disbonding of an internal surface.
--NTSB Safety Recommendation, March 24, 2006
It should be noted that Airbus has long denied that internal damage to composites can remain visually hidden yet compromise the integrity of the structure significantly; they have also rejected the possibility that internal composite damage can “propagate” (a condition known in some cases as “composite fatigue.”) Also, the “tap” test indicated, in this case by the NTSB, is the type of “visual” test on which Airbus has relied as the standard for their maintenance inspections and the type of inspection that we warned was often “ineffective” in our 2002 letter to the NTSB & FAA.



>>>There are no silver bullets and no single test is the optimum choice for all situations. While you seem to have a problem with visual inspection, that is probably the most important and most useful method available. After all, isn't that what a walk-around inspection is?<<<

Ok...I do a walk-around on my A300 and see a bubble on the underside of the elevator? Do I go? The answer was always "yes"...because when they "fix" the many, many cases of water penetration into the layers of composite on the A300s, they do not "buff out" the repair, but simply leave them "bubbled". So...it is impossible to tell if one is new or "fixed". Visual inspection is fine...but the question is, "is visual inspection adequate to find all interior damage on composites?" That answer is "no" and that means we are flying around in damaged aircraft, as AA 903, Air Transat and Fed Ex have already shown.

>>>The tap test used to be the primary means of testing composite structure. While there have been several new and more accurate NDT methods (such as I listed earlier) to determine the structural integrity, the tap test is still considered a valid means to discover certain types of of flaws in composites. Often when a component fails a tap test the next step is to follow up with a more comprehensive (and complex) test.<<<

Please explain, then, how AA 903 went for five years without discovering the crack in the aft lug of it's vertical fin, that once discovered using ultrasound, resulted in the immediate grounding of the aircraft by the FAA (see NTSB testimony in AA 587 hearing) and the immediate removal of the tailfin by AA? That jet was grounded almost two years and the rumor is that Boeing crafted a tail to get it back in the air because Airbus refused to replace it--they wanted it to fly with the crack.

>>>And while you are right about eddy current testing being a way of testing aluminum structure, it is usually only when specifically mandated by either a maintenance task card, AD, service bulletin, or by engineering. Most structural discrepancies are discovered by the old Mk II eyball.<<<

I can tell you that airlines who rely on the first indication of a problem be seen by some mechanic or pilot on a walkaround...are just waiting for another catastrophe. It is obvious that periodic inspections MUST include some sort of NDT...and I know for a fact that some are included (ex. A320 uses ultrasonic on the fuselage ribs and flooring).

So...if you are saying that is not the case, then you--and we--ought to be concerned...and vocal--about that failed policy.

Jetblaster