GAMA and FAA: in talks to explore changes to Part 23 Certification 4

[Sparweb]

What can I say? The backrooms of numerous repair shops are stocked with plastic airplane wings they can't fix. They need OEM engineering support for repairs because the scope of damage exceeds the MM limits. They wait and wait because the queue is very long. The work could be done, but the approved procedure, drawings, materials, processes all need detailed evaluation and documentation before the wing can be airworthy again.

I have been whacked by FAR 25/23/27/29.613 enough times to be wary of composites. Maybe I'm just unlucky, but the airframe types I've been dealing with don't use materials in Mil-Hdbk-17. No data, then no proof, so no approval.

Since I am not the OEM, I don't have the proprietary data on hand to back up analysis of a repair. To get it would cost as much as a new wing. To develop the data would cost more than a new wing. The client buys a new wing.

I'm not talking about dropped screwdrivers, either. Everybody reading this thread knows you can find that kind of repair in the Maintenance Manuals of any aircraft. I'm talking about hangar rash that cracks the LE. Birds nests in the landing gear well. Fuel seepage. Disposition after a lightning strike. All the fun stuff that happens to airplanes in their lifetimes. That doesn't get written up in the MM because every case will be different.

Nobody can cope with these repairs unless they have access to coupon strength/humidity/temperature test data. As I said, that belongs to the people who developed it for the type certificate.

To make statements that "it's easy" means you either you work for an OEM, have a deal with one to license the data, or acquired the data by "other" means... and I'll leave it at that.


Steven Fahey, CET

 

[berkshire]

Sparweb.
I agree with you.
When I shut down my repair station I had 11 plastic wings from various manufacturers that were unrepairable because the repairs needed were outside the scope and detail of the maintenance manual (We burned them.), and it was cheaper to buy a new wing than engineer a repair. Another thing driving this was the customer who very often felt that a new wing would just be better than one that was fixed.
Right now in the USA there is one manufacturer of plastic single engine land aircraft, who is charging far more than cost for engineering expertise for relativly simple repairs that are outside the somewhat limited scope of his repair manual, just to ensure that damaged aircraft are totaled out instead of being repaired.
B.E.

The good engineer does not need to memorize every formula; he just needs to know where he can find them when he needs them. Old professor

 

[thruthefence]

"Designing repairs" has become a profit center for the oem's, "plastic or otherwise.

Had a "plastic" aircraft attempt to taxi with the tail tie down still attached, damaging the attach point. The repair (and associated paperwork) cost thousands of dollars to acquire.

At the time of the incident, the type was in the field for years. You can't convince me that that this hasn't happened before. If so, and the data was approved, why wasn't the repair scheme added to the maintenance manual?

Because all you have to do is double click a file, and send an invoice for $1500.00, and the end user has to pony up the money.
Cha-Ching!!!

 

[berkshire]

Through the fence
Most of my experience has been with German (Plastic.) aircraft where repair schedules came with the necessary spare parts at a reasonable price, and if the manufacturer said it was cheaper to produce a new wing than engineer a fix for the broken one I believed them.
Your case in point is what I am talking about.
A relatively simple repair of a type that is likely to happen again should be added to the repair manual.
B.E.

 

[blakmax]

Well people, there is a report floating around of FAA concerns about composite repairs for the 787 aircraft

"In a report (PDF) completed last month, the U.S. Government Accountability Office examined "safety concerns" about the use of composites in commercial aircraft. Based on research and interviews with experts, GAO investigators identified four key safety-related concerns with the repair and maintenance of composites in commercial airplanes, but added that none of the experts they talked to believed these concerns were insurmountable or posed "extraordinary safety risks." The FAA is taking action to help address its concerns, the GAO said, but added that "until these composite airplanes enter service, it is unclear if these actions will be sufficient.

The four concerns cited by the study are: (1) limited information on the behavior of airplane composite structures, (2) technical issues related to the unique properties of composite materials, (3) standardization of repair materials and techniques, and (4) training and awareness. Boeing's 787 is the first mostly composite large commercial transport airplane to undergo the FAA certification process. Since existing safety standards are often based on the performance of metallic airplanes, the GAO said, the agency was asked to review the certification processed used by the FAA and EASA. The 787 is about 50 percent composite by weight, not counting the engines, according to the report"

It appears that your concerns (berkshire and through the fence) about repairability of composite structures is supported at a high level.

My background is in the development of bonded repair technology for composite repairs of metallic structures. This technology has a proven history on military aircraft extending over 36 years with high reliability, substantially better fatigue performance compared to mechanical repairs, better NDI and demonstrated cost savings. Even with this track record, the number of bonded repairs included in repair manuals is incredibly small.

I am not sure if this and the repairability of composite structures are due to characteristics of the materials and technology, a lack of understanding of the specific requirements for repair of new materials, a lack of intestinal fortitude in development of repairs or just commercial opportunism by manufactures in wanting to make the most of a lack of operator capability in the field.

Clearly, these are important issues and need to be resolved if composites and bonded structures are to achieve their full potential.

Regards

Blakmax

 

[SWComposites]

The report mentioned by Max was not written by the FAA, but by the GAO which are a bunch of bureaucrats whom have no freaking clue what they are talking about; I am not aware of any certification or composites engineers working for the GAO. Their "experts" are probably from academia who are not aware of what is being done within Airbus and Boeing.

"the number of bonded repairs included in repair manuals is incredibly small" - is not correct; there are lots of bonded repairs included in every Boeing SRM from the 737 thru 787.

SW

 

[blakmax]

SW Thanks for the clarification on the report and the status of the authors.

I needed to be clearer about bonded repairs in SRMs. There are many bonded repairs for honeycomb sandwich panels, but the number of repairs for non-sandwich structure (for example wing or fuselage skins) is extremely low.

Regrads

Max