787 fastener issue on wing

[CONSO]

Feb 23 The U.S. Federal Aviation Administration proposed a new airworthiness directive (AD) for some of Boeing Co's 787-8 Dreamliner aircraft after a report found a defect in a wing component.
The report said certain web fastener holes might not have been deburred properly when manufactured.
This can develop fatigue cracking and weaken the primary wing structure so it cannot sustain limit load, the FAA said.
The AD, effective March 9, required revising the maintenance or inspection program to include an airworthiness limitation for repetitive inspections of the web fastener holes in the overwing flex-tees, the FAA said.
Boeing was not immediately available for comment. (Reporting by Arunima Banerjee in Bengaluru; Editing by Maju Samuel)
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FWIW- deburring holes is more critical in metal parts thann in composites- but even so, the argument that lack of deburring or incorrect deburring causing a fatigue problem is very unusual . One possible fix would be removing fastener, coldworking the hole ( using a sleeve mandrel operation to stress the hole, reaming to the next size and instaling a new fastener.



For those not familiar with the term coldworking- suggest you look up Fatigue technology cold expansion. The process is simple during manufacturing but a bit more difficult after assembly. Stressing the hole as described to improve fatigue is NOT intuitive. That technology was developed in boeing in the late 60's, and used in every plane starting in the 70's. The 767 used it extensively on most all major wing components skins, spars.


How do I know all this - in the 60's, my deskmate was the guy who developed it,( lou Champoux ) and I was very much involved. A decade later I developed a smaller tool to allow installation in more places . ;)



My guess is the metal parts used to spread out the stress where the composite wing structure joins the wing center box.

[Wangler]

I would be surprised if the holes weren't already cold expanded in production.

Of course, one would expect them to have been deburred then, too.

[Yankee Whisky]

Is there not a drill that also incorporates the de-burring bit ? Two steps in one. Or is this subject to another problem ?

[CONSO]

Is there not a drill that also incorporates the de-burring bit ? Two steps in one. Or is this subject to another problem ? There are essentially 3 locations for burrs. ( re metal structure ) Composites have similar issues but usually not as significant. This subect is about metal

1) exit burr 2) interface burr [ if parts are NOT well clamped together when drilling] 3) Entrance burrs

1) Exit burrs can keep fastener collars from seating properly, but are often difficult to access and remove depepndinbg on structure. Many types of fastener ' nuts' ' washers' ' collars ' allow for small burrs via a ' recess '. And in other cases, burrs are put into compression when ' nut' or collar is tightened down.

2) Interface burrs unless extreme enough to prevent parts to clamp up or mate are rarely a problem as they are also in compression in most joints Those burrs can be generally contolled via choice of drill bit configuration, reaming, and feed rates or a combination thereoff

3) Entrance burrs can easily be removed by hand and or power tool and /or tool/drillbit bit configuration - but may require a second operation. However if hole is drilled from an outside surface, usually the hole is countersunk, either by a second operation, or by combination drill csk tools carefully adjusted so as to leave a flush surface when a csk fastener is installed and tightened. Tolerances of a few thousandths of an inch in csk depth are routine. For such holes, entrance burrs are NOT a problem.

Interior fasteners are usually not countersunk and while deburring can be an issue, by not allowing fastener head to properly seat, or to be sealed ( fuel tight/corossion,) almost any casual inspection visual or by feel ( careful not to cut thumb or finger if excessive burr is usually sufficient.

What is puzzling re the supposed burr issue is that burrs of types 1) 2) and 3) when fastened and torgued are usually in compression and not in themselves a fatigue problem. But if they are so great as to keep fastener from propely seating, or give false torgue values causing fastener to not be properly seated and screwing up design load transfer across a given joint- THEN there is cause for concern. Without detail information as to the proposed AD, any further discussion on cause, effects, cures, methods is near worthless.

I have tried here to give a very simplistic explanation of fastenin issues- which as much art as science and has been well researched for decades.

Bottom line - while I suspect a cost saving issue in assembly may really be the problem- thats MY unsupported opinion. Nuff said:ugh:

And here is a bit more

Only applies to two airplanes ! ??


DEPARTMENT OF TRANSPORTATION Federal Aviation Administration 14 CFR Part 39 [Docket No. FAA-2016-3699; Directorate Identifier 2015-NM-109-AD; Amendment 39-18402; AD 2016-04-08] RIN 2120-AA64 Airworthiness Directives; The Boeing Company Airplanes AGENCY: Federal Aviation Administration (FAA), DOT. ACTION: Final rule; request for comments. ----------------------------------------------------------------------- SUMMARY: We are adopting a new airworthiness directive (AD) for certain The Boeing Company Model 787-8 airplanes. This AD requires revising the maintenance or inspection program, as applicable . . .

(c) Applicability

The Boeing Company Model 787-8 airplanes, certificated in any category, having line numbers 78 and 82.
(d) Subject

Air Transport Association (ATA) of America Code 57, Wings.
(e) Unsafe Condition

This AD was prompted by a report that certain web fastener holes in the overwing flex-tees at the wing-to-body interface might not have been deburred properly when manufactured. We are issuing this AD to detect and correct cracking in the web fastener holes in the overwing flex-tees, which can weaken the primary wing structure so it cannot sustain limit load.

[b1lanc]

Interesting that only 2 AC are involved. As I recall, all wings were/are manufactured by Mitsubishi Heavy Industries and fastener issues (not necessarily burrs) have been a problem on multiple occasions (lack of fasteners, non-aerospace fasteners, incorrect fastener installation, forgotten shims.....

[CONSO]

As I recall, all wings were/are manufactured by Mitsubishi Heavy Industries

Correct- but the area mentioned is where the wings are attached during assembly to the 'wing box ' and done at the factory during final assembly.

That area has always been a difficult to join area, and is essentially the location of previous 787 wing problems during structural tests- and if I understand just what parts are involved, they were a major issue in the first few 787 built. And the AD numbers of $80 85 dollars to fix/correct is IMHO a bit phony..