One-time STC Development

[CamTom12]

I think Stephen has done a couple… anyone else? What all goes into that?

I was considering purchasing an Experimental-Exhibition certified airplane but a talk with my FSDO made me uncomfortable with that.

Got me thinking though. Say, for example, than an airplane existed in 100% TC and STC compliance except for the engine/prop. Imagine the engine/prop were both from other TC’d aircraft and that this combo had flown together for 30+ years.

What do you think the odds/level of effort would be of getting a one-time STC for the engine/prop and bringing the whole airplane back into a standard airworthiness certificate?

Or is that a complete non-starter due to some reg I’m not familiar with?

Not a project I’m planning to undertake, just got me curious about the possibilities.

[dgapilot]

For any STC, you better plan on at least 2 years. My PA-16 gross weight increase is at about 2 1/2 years now and still a long way from completion.

This guide will walk you through the application part of it https://www.faa.gov/aircraft/air_cer.../cpi_guide.pdf

The biggest issue is developing a compliance document. You start with the certification basis for the airplane, and determine every regulation that the original design met during the TC process, and then identify every regulation that the new installation changes how the original TC showed compliance to. Once you have identified all those regulations, then you need to figure out how the new installation will show compliance. Each one will be by analysis, test, or any number of other methods. Once FAA agrees with that compliance checklist, then you have to develop the data necessary . In most cases you will need to hire one or more DERs to review and approve that data ( you can also hire them to develop that data as a consultant). Once the data is approved, then you need to actually fabricate what ever parts are needed, and then hire a DAR to conform those parts to the design you come up with.

In short, it is not an easy process. Depending on your engineering expertise, you might get away with as little as $2500, but could easily run up around $100k or more if you need to hire out all the engineering.

If you are only looking at a 10% increase in HP, it could possibly be done as a Field Approval. Any greater increase beyond what the TC authorizes has to go STC. At the very least, you are looking at a Structures DER, a Powerplant Installation DER, possibly a Flight Test Pilot DER and a DAR.


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[Stephen]

I agree with dg. It is not cheap if engineering is necessary. You can't just beef up the structure and call it good. Uping the gross weight means that you multiply that increase by 3.8g plus a safety cushion. Every part of the plane effected needs to be analysed and likely tested. I got my first one time stc approved converting my Pacer yokes to sticks only because I used the PA 16 design which Piper had already tested. It was done years ago and I was very lucky to get an FAA engineer who was cooperative. It will not happen again. Later I spent 6 years trying to get a one time stc approval to move the ailerons outboard and expand the flaps on my Pacer.I have some engineering ability and did my own calculations plus I had an aeronautical engineer DER advising me. The FAA was helpful but the higher ups were not comfortable without it having an engineer stamp. When I thought I was getting close they added new demands including a wing load test. This would require the destruction of a wing. Plus the flight tests they wanted in my case required a FAA test pilot and the plane equiped with a spin recovery shute. I spend a few thousand dollars but, it would have required much more....all for a one time stc. BTW, a one time stc technically has to meet the same requirements of a multiple STC.

I suspect that if someone wanted to spend the money they could get a multiple stick conversion stc if you had installed the Trimmer PA 18 gear. The Clipper sticks would fit in easily with the bungees removed. But, I doubt there would be much market.

[Steve Pierce]

Been dealing with the FAA for 2 weeks on the Sensenich ground adjustable prop. I would avoid them like the plague.

[Jeff J]

I did it to a PA20 about 20 years ago. The engine was approved for the airframe via one time STC with a constant speed prop. I swapped the prop for a fixed pitch approved for the engine. It took me about 6 months to get approved for the combo on the airplane through the FSDO and engineering. About a month of it on a flight manual supplement that really didn’t change anything. As I recall, it was an O-320-B3B with a Sensenich 74DM.

[Jeff J]

I came back to fix my previous post but don’t see an edit option. I did not actually do an STC. Mine was a field approval to alter the one time STC. It wasn’t a popular idea with the FSDO but they were helpful about getting it done.

[dgapilot]

I've done 2 one time STDs, both several years ago and booth took almost a year. I'm in the midst of an STC now for PA-16 and I'm over 2 years into it. It is not easy or cheap!