Help on disposition!

[KANSASENG22]

I have a rivet hole for a standoff (wiring)that has been mis=located and now a .128 diameter hole is in the radius of a machined beam, The beam is on a pressure bulkhead, the flange common to the radius would be mostly in tension. The beam flange is .300 thick, radius is .38, beam material is 7050 machined plate, Thanks for any help.

 

[tbuelna]

Your disposition options are use as is, rework, or scrap. The 7050 material is not weldable so the mislocated hole will likely have to remain. If it is acceptable to use a wiring standoff located in the out of position hole, or there is sufficient material remaining to drill another hole in the correct location, then in either case you will need to get stress approval. Have QA thoroughly document the discrepancy, write up your proposed corrective action, and submit them to stress.

 

[rb1957]

you could fill the mislocated hole with a freeze-fit plug (of 7050T?) and probably relocate the stand-off so it doesn't interact with the plug.

another day in paradise, or is paradise one day closer ?

 

[KANSASENG22]

I do have enough room to plug and relocate to dwg location. I will take a fatigue hit so it is now in Stress for validation. Thanks to everyone.

 

[WKTaylor]

KansasEng22..

IF this is a new acft, then extreme measures may be required to attain full/normal operating life.

IF a repair doubler is needed to resore strength or fatigue durability, then integrate it into as many existing fastener holes as possible. Some times just adding fasteners/holes for a repair in a fatigue or stress spensitive area can create all sorts of secondary problems.

NOTE.
A repair to a new part in a new acft may even be in-adviseable simply because a new 'XXXXXX' should not need a major repair before it leaves the factory. The first company I worked for would NOT allow major repairs on any new machined component... especially on fatigue or strength sensitive parts/assemblies that might need on-going 'special inspections' to re-validate airworthiness. Our liaison Mantra was 'remove and replace' if any significant repair [other than OS fasteners] was required. Occasionally we were authorized by managers to repair 'XXXXXX' and then rout it to 'spares' where minor/major, repairs, etc were 'OK' from a customer persopective... especially if the part/assy was sold at a 'discount'.


Regards, Wil Taylor

o Trust - But Verify!
o We believe to be true what we prefer to be true.
o For those who believe, no proof is required; for those who cannot believe, no proof is possible.
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion"]
o Learn the rules like a pro, so you can break them like an artist. [Picasso]

 

[tbuelna]

wktaylor- In my experience, manufacturing always prefers to do whatever they can to keep from scrapping any part/product. Especially a part/product they have invested lots of time and money in producing up to that point.

A while back I worked on a R-R commercial engine program. After certification testing was completed, the serviceable test engines were refurbished and sold. Earned a couple million dollars per engine for the company. The refurbed engines were acceptance tested and sold with a warranty from R-R.

Back in the late 90s while working at Boeing Renton, there was a situation where the over wing emergency exit openings of one 737 model were slightly smaller than required by the FAA. By the time the problem was caught there were already new aircraft ready for delivery. The customers would not accept the aircraft until the problem was corrected, so there were quite a few new 737s stacking up outside waiting to be reworked. Between the cost of installing new emergency exits and financial penalties for late delivery, the cost per aircraft was likely a couple million dollars. The rework involved adding pieces of structure that were not used on later airframes manufactured to a revised design. There was no way Boeing would scrap the discrepant new airframes, even if it meant spending a million dollars or more per aircraft to fix them. The customers were happy to accept the reworked airframes since they received substantial financial compensation from Boeing in return.

 

[rb1957]

well, yes, it depends on what you're talking about ... a fitting or a fuselage. The cost of a fitting probably doesn't justify significant rework cost; the value of a fuselage (if only from it place in the "sausage machine") would justify enormous rework.

If you anticipate a fatigue "hit" ... I'd suggest, if the hit is more than desirable, to use some fatigue improvement ... higher interference, freeze fit plugs, shot-peening ?

another day in paradise, or is paradise one day closer ?

 

[tbuelna]

The situation I described above involving replacement of overwing exits on brand new 737s required enlarging the opening in the fuselage by around 1/2". Some reinforcements were probably necessary to compensate for the enlarged opening, and these likely added a bit of weight, but I don't imagine the retrofit resulted in reduced fatigue life.

All of the retrofit 737s were delivered to customers. But consider the situation with some 787s, where the first half dozen production aircraft were ~5,000lbs over spec weight. These aircraft were not accepted by their customers, who instead opted to wait for an updated 787 that met the weight spec. Instead of reworking the overweight 787 airframes to meet the weight spec, Boeing chose to try selling them as is for a discount. Last I heard the overweight 787s were still owned by Boeing and waiting for a buyer. Unlike the 737 example, this is a case where the cost of reworking a non-conforming airframe with very high value could not be justified.