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Qantas Airbus

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dik

dik

Structural
Apr 13, 2001
25,837
Air safety investigators in Australia say they have identified a serious manufacturing fault with engines fitted to Airbus A380 passenger jets.

A misaligned component of the Rolls-Royce Trent 900 engine used on a Qantas A380 which exploded last month thinned the wall of an oil pipe.

This caused "fatigue cracking", which prompted leakage and ultimately a fire.
 
The way I heard the report, the oil pipe itself was manufactured with the wall thinner on one side. Something about the pipe being reamed, and the reamer was misaligned. Does that sound like a normal manufacturing procedure?
 
Not where I come from, but those aero boys always have us in stitches with their whacky manufacturing methods.

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376
 
"The problem relates to the potential for misaligned oil pipe counter-boring, which could lead to fatigue cracking, oil leakage and potential engine failure from an oil fire within the HP/IP bearing buffer space," the ATSB report said.
Click to expand...

Pretty vague description.

The whole store, such that it is, is here
Please remember that mostly everything reported by the press is wrong.
 
from Flight International site ...
"Further examination of the cracked area has identified the axial misalignment of an area of counter-boring within the inner diameter of the stub pipe; the misalignment having produced a localised thinning of the pipe wall on one side. The area of fatigue cracking was associated with the area of pipe wall thinning."

doesn't sound like a manufacturing error ?

also sounds odd (that a misalignment would cause localised thinning) ??

 
I know little of aircraft, but the thinning may have been caused by misalignment during fabrication? Thought it was interesting that they had found a possible problem... and, yes, I have a healthy caution for articles in newspapers

Dik
 
The ATSB has a special gift for obfuscatory language.

Trying to put these little snips of disinformation together, it seems that there is a design requirement to bore out the ID of a tube or pipe for some length.

Why anyone would think this is a good idea is beyond me.
 
maybe it was an assembly/installation MRB ... that maybe somebody regrets now ?
 
So, it sounds like a 'counter bore' wasn't adequately aligned with the OD of some kind of 'pipe'. Remember what the press is calling a pipe, may not be what some of us think of as a typical pipe - it may be some kind of custom fitting or something, not an off the shelf piece of 'pipe'.

This could be a design documentation problem - perhaps the coaxiality of the counterbore to the OD wasn't properly specified. This requirement is often overlooked on drawings, people often assume that because diameters are shown coaxial in the drawing that's enough, however ASME standard explicitly says there is no implied alignment - you need to explicitly specify how coaxial they are. I'm not sure how ISO may differ from ASME on this though.

Or it could be a manufacturing problem, the part wasn't to print (MBD whatever) and the QA process didn't catch/prevent it.

Or it could be design problem - the alignment required isn't feasible - though I doubt this.

Or we could be missing a whole bunch of info and it was something else entirely.

Posting guidelines faq731-376 (probably not aimed specifically at you)
What is Engineering anyway: faq1088-1484​
 
Hmm, I'll be interested to see the outcome on this.

One suspects this component may well not have been a completely in house manufactured RR part. Even if their drawing/MBD, its manufacture may well have been sub contracted.

I wonder if it will end up as one of the samples of 'why the drawing needs to comply to drawing standards' etc.

Posting guidelines faq731-376 (probably not aimed specifically at you)
What is Engineering anyway: faq1088-1484​
 
The c-bore looks like what you get when somebody bumps the table of a milling machine holding a simple fixture, and nobody notices for a while.



Mike Halloran
Pembroke Pines, FL, USA
 
Some inspector some where bought off that part. However, it may be that the inspection criteria did not look for that issue, which means the root cause would be farther back in the design and manufacturing interface. In other words, there should have already been inspection criteria in place to catch this. If it was in place, who ever signed off the part has a serious problem with retaining their inspection position.
 
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