Any Materials Scientists in the crowd?

[catmandu]

MT Natural Composite (Carbon over wood) propeller on an experimental airplane.

100 hours of use, it sat crated for three out of four years in a conditioned hangar. It would continue to be hangared in the dry southwest after installation and use for the next two years.

Would there be any material concerns flying it past the manufacturer mandated 6 year overhaul, assuming it was found to be otherwise airworthy?

 

[Mtns2Skies]

No concerns. Fly it.

@CC268 did materials before his exodus from engineering.

 

[donjohnston]

TLDR - My MT prop is 14 years old. Still flying strong.

MT Sucks.

My MT prop sat for about 5 years in a climate controlled shop. Then on the plane for a year and they flew for 2. I contacted MT and they "Your prop is not airworthy. You must ground your aircraft immediately." Because it was past their overhaul interval. And to plan on it taking 3 months (or more) to overhaul. I pointed out that my plane was experimental and they could pound sand.

Also said that the damage that was repaired made the prop not airworthy. Even though it was repaired by guy whose repair procedure was copied by MT as their guide to repairing blade damage.

I was next on the list for a Catto prop before I sold the plane. If I had kept the plane I would have set fire to that prop out of spite.

 

[Ted]

Keep in mind that Hartzell and McCauley generally have a 6-year TBO as well. For Part 91, it's not required (E-AB or not). 135 is different. We ran into this a lot. So in that regard, MT is not different. What is different is I think the understandings of the respective companies with respect to operation under Part 91 in the USA.

Someone more familiar with the workings of operating under EASA vs FAA can probably go into better detail than I can, but it seems that in Europe the idea of mandatory replacements/overhauls for Part 91 is accepted. I've come across this same attitude with other OEMs as well who think that they can enforce a mandatory replacement hours/time, not realizing that they can't force that upon Part 91 operators here in the states. Of course some things are required, but there are a lot of items that are optional for us here.

It wouldn't concern me to fly one past the 6 year interval.

 

[Bell206]

Would there be any material concerns flying it past the manufacturer mandated 6 year overhaul, assuming it was found to be otherwise airworthy?

No. Its no different than any other OEM recommendation. However, with any composite component know what to inspect and how, like a tap test. Here are a couple MT docs on field repairs that will give some insight on what to look for. The key is to make sure all the composite is still bonded and solid. I believe there are other docs as well. MT props are pretty bullet proof.
https://www.mt-propeller.com/pdf/sls/sl32r8.pdf
https://www.mt-propeller.com/pdf/sls/sl32-1.pdf
https://www.mt-propeller.com/pdf/sls/sl32-2.pdf

but it seems that in Europe the idea of mandatory replacements/overhauls for Part 91 is accepted

In general, yes. Unfortunately, there is no singular equivalent to Part 91 GA aircraft in the EASA world. Its this different world that drives people in the EU to use an N reg whenever they can to maintain their aircraft. It goes back to the JAA days when only the OEM could issue and approve all the support and mx documentation for an aircraft. No external STCs, field approvals, etc. in those days which gave the OEMs a gold mine on all aspects. There have been some changes with the EASA but they are still no where close to what we have here.

 

[Ted]

In general, yes. Unfortunately, there is no singular equivalent to Part 91 GA aircraft in the EASA world. Its this different world that drives people in the EU to use an N reg whenever they can to maintain their aircraft. It goes back to the JAA days when only the OEM could issue and approve all the support and mx documentation for an aircraft. No external STCs, field approvals, etc. in those days which gave the OEMs a gold mine on all aspects. There have been some changes with the EASA but they are still no where close to what we have here.

That makes sense, and explains the different viewpoint.