Cracked means that the aircraft gets grounded until it is repaired, so I assume it affects structural integrity.
IMO the FAA should remove the 90,000 cycle designation from the 737NG and install an inspect and repair regime instead. This first AD regarding inspection is in reality just to get an measure of the severity of this problem.
There will be more ADs, the inspection intervals will shorten. But removing the 90,000 cycle life? Have we proven it isn't a manufacturing issue?
The A380 and A320 both were found to need wing reinforcement. The 60,000 cycle limit wasn't removed for the A320 or 36,000 for A380. Instead a repair was approved. New build aircraft are built to a certified modification. Or Embraer wing spars. Or...
There will be a temporary repair approved. There will be a permanent repair approved less than replacing the pickle forks. It will take a few years, but Boeing will get back to full duration on these.
The A320 did not start out with a 60,000 cycle limit. The original approved limit was 48,000 cycles and 60,000 hours. The limits were extended after further fatigue testing and checking of frames reaching the early lifetime limits. The wing cracks on the A380 were found due to the fatigue testing. It would be interesting to get a reference to wing cracks on the A320, as I have not heard of that.
The 737NG got its lifetime limits out of the box. The pickle forks are part of the lifetime parts, no limited lifetime expected. no checking regime, but the current AD, in place.. Cracking was not found through fatigue testing, but by chance at the conversion of older 737-800 to freighters.
It was played down as A320 corrosion.http://i.stuff.co.nz/business/3402061/C ... rbus-wings
This was found after the 60k extension.
Airbus didn't find their issue in fatigue testing either and far earlier than 48,000 cycles. The Airbus finding was a surprise. It turned out island hopping was brutal on A319/A320 family wings.
My point is that there will be a repair. The regulations do not specify how a problem is found. The first finding was at about 36,000 cycles. The pickle forks with a life of 90,000 cycles must be inspected every 30,000 cycles.
The fact there are so many found after 35,000 tells us these passed. Now the low cycle incident is of concern.
So for now, ground if cracks found and increase inspections. 25 findings out of 500 is bad, but not unprecedented.
There will be shorter inspection intervals until a standard repair is found that returns the life to design.
That repair cannot happen until a new stress analysis is performed. Just as a temporary repair will be found.
There is a process. The cycle test was with a maximum allowed stress (it is well known for aluminum vs. cycles for life). Just knowing the youngest happened at 20,600 cycles and many later tells us the actual stress level. Boeing has good stress engineers that will find a permanent and temporary repair.
The A380 wing cracks are an example. They happened incredibly early. Well before the inspection. Only found because of a RR uncontained engine failure.
The process is intentionally non-punititive to have self disclosure. The was a 738BCF where that self disclosure found the problem and created the AD.
There is a checking regimen. Every HMC. If you cannot inspect visually, x-ray. I assume the HMV required inspection might be altered/improved.
I'm not sure what you are trying to imply.
Legally, there was a self reported finding. The FAA issued an AD on inspections. The data from those inspections will result in a new AD on modified inspection intervals.
Rework is always an approved repair (return to drawing) or pickle fork replacement.
Permanent repairs take time.
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