Serialized STC prop approvals

[PilotDAR]

Ready for a long read?....

I'm asked from time to time to approve a different prop on a GA airplane by serialized STC. In it's most simple form, this was work within my delegation, and TC left me to do it. Recently, new TC staff have delved into "how" I find compliance, particularly that there has been no acoustical change to the plane, and this has brought this work to a stop for me. Personally, I'm not terribly concerned, as both my planes have propellers, and I have no need to change them, but I know that the approval of replacement propellers is vitally important for some owners, particularly when the prop they have fails, and there is no approved replacement available.

Historically, I attended the TC CARAC meetings in Ottawa about 25 years ago, when the first "516 Emissions" standards were presented for comment. This new standard would capture the noise effects of propeller changes, and align the requirements with [what is now] EASA requirements. I presented my objection to this new burden on GA plane owners, who might want to change props in the future. I was sitting beside Adam Hunt, who was representing COPA. I said "Adam, you have to write an article in the COPA magazine, explaining this, and alerting members to the possible effects, so they can object - crickets. I contacted a few local groups and AMOs, no interest. I wrote a letter to TC asking that all planes of 300 HP or less be exempt. I was told months later by the CARAC Chairman, that mine was the only letter of objection to the new 516, so it was enacted.

Happily, along the years, TC Engineers I previously worked with to issue STC's for prop changes were no too demanding about assuring noise compliance, so approvals found their way through. A few years back TC started to notice this more, and it became wise that I document how I justify "no acoustical change" for most of these approvals. (I have obtained two exemptions from the regulation for clients, and done one full blown, EASA compliant, TC witnessed noise test, and have the data - 128 amphib, O-550, MTV9 prop).

So in November 2018, my TC Engineer and his boss in Toronto were joined by two very senior TC Aircraft Certification staff from Ottawa and I met. We agreed and documented my means to justify how I approved these, and limits within which I could issue these approvals without overt TC participation for each approval. Early this year, a newer TC staff member reviewed this, and got thinking, and contacted TC in Ottawa to inquire - and got a different answer. So I was told to stop - in the middle of three prop approval projects. I complained bitterly - delegation removed, why?

Yesterday was the big teleconference call, six TC senior staff, and I, including three of the four from November 2018, to recount history. The formal position of the TC Powerplants group is that each propeller change should show compliance = noise test = really costly, and very hard to arrange. I explained that this did not suit the GA industry need. I would like to continue to find compliance with a preagreed rationale. The senior TC staff involved very much supported my using a practical, low cost methodology, to encourage owners to actually have the new props they want to use approved.

The end of the call has left a cracked open path for me to follow, so I'm going to make another proposal to TC about this. A part of this will be blade number increases. I had two days of training about noise compliance with EASA in Cologne Germany many years ago, to assist me (and they certainly did) with the noise testing I had to do for the 182 amphib. I did the full EASA test on the 182, and TC witnessed it. I got all of the data. This included doing passes over the microphone at different RPM settings to compare.

Of interest to readers here would be that the MTV9 prop is already approved by two STC's. One (EASA STC) has an RPM limit of 2500, and the other (FAA STC) for the same prop, same engine, same 182, has an RPM limit of 2700. Of course the 2700 RPM FAA STC is more popular here in North America. I can say, with extensive test data on that plane, 36 qualifying overflight passes, that the difference in altitude 2 km from brake release, between a 2500 RPM climb, and a 2700 RPM climb, all other things being equal, is 60 feet. That extra 200 RPM is making a lot more noise than climb. So the plane was approved at 2550 RPM, which met the EASA noise requirements, as the planes was being modified for export to Norway. TC does not issue noise certificates, but I issued my serialized STC for it, which included 27 other mods.

Several years later, the owner and I landed it at a resort island in northern Germany. We were warmly greeted at the FBO, and kindly asked for the noise certificate for the plane - Ummm..... Then I recalled that when I wrote the Flight Manual Supplement for the plane, I had written in the limiting RPM, and noise value. I went to the plane and got it, and sure enough, TC had stamped "approved' on that page. The FOB fellow accepted it. Our landing fee was thus 20 Euros. I asked what the landing fee would be without the noise certificate - 200 Euros. This is why European owners can justify buying the expensive prop and exhaust, they get a noise certificate with them.

Canada is not completely conforming the EASA/ICAO way of doing this, but their pointed that direction, and without a push from the GA industry, it's going to creep more that way. I'm working to maintain a cost effective [possible] means to approve prop changes. So I'm doing my homework for a good proposal. I am pleased to say that TC is at least listening to me....

[photofly]

You are doing the Lord's work for the GA community.

[digits_]

Thank you for fighting for general aviation during those battles I didn't know existed!

[JasonE]

Excellent work Jim! Recently I have been flying in more 3 bladed types and sure can feel/hear the difference from a 2 blade. As you know, I don't have much love for a particular 2-blade.

[PilotDAR]

Just to bring interested owners up to date: As of this morning, I have been informed that propeller approvals involving a change to the "type" of propeller, or the number of blades will require a noise test, unless TC agrees otherwise. And, most modification projects involving an external mod to the plane (other than a float installation) will require a TC evaluation for possible effect on noise, and requirement to noise test. I've done a noise test, and it's a big deal.

For propeller changes, the only changes which can be expected to be allowed without a noise test: Same or smaller diameter, Same or slower RPM, Same number of blades, and Same type of blades (for example not a composite MT replacing a metal prop). Both TC and I have dozens of hours confronting each other on the massive inconvenience of this to the GA fleet. TC Ontario region has expressed understanding of the concern. TC HQ Ottawa is defining more clearly the standards they expect to see followed.

Some of what I used to approve will no longer be practically possible, other will become more expensive. Mods wholly inside the cabin are not affected.

[photofly]

Out of curiousity, what's the bill for a noise test for a piston single?

[PilotDAR]

When I did a noise test for EASA compliance for the 182 amphib (with EASA's pretty good support), the cost came to around $17,000. It could perhaps be done at a lesser cost, though for that test, everything came together as planned, as opposed to having a missed, or incomplete test due to changing weather. The test must be done in less than 3 knots wind, and can take an hour or two of over flights. There's fairly involved post test data processing too. It's not just standing at the end of the runway with an Iphone...

[photofly]

Is there a way to advocate for a simplified nose test procedure? I can't imagine the various MT dealers are very happy about this.

[Beefitarian]

Does Transport require a noise test for every propeller or is it per type?

If it could be done once for a particular three blade propeller that would be replicated, it seems like a propeller manufacturer might have more to gain getting their products tested so we could just buy them certified. Thus spreading the cost over a few hundred units.

[photofly]

This is for a serialized (single aircraft) STC. MT and others have a bunch of STC's for prop changes on popular types with stock engines, but if you have an unusual type and want a different prop, or an old type for which the original prop isn't available (does this happen) then you need a custom STC for your one aircraft, and you get in touch with PilotDAR.

[Beefitarian]

Ok, so follow up questions.

How big is the difference between several propellers that are the same length and pitch?
If you test a constant speed propeller is there a range of sound volumes?

[JasonE]

This is another expensive blow to the G/A fleet. It seems like TC is going backwards these days instead of forward.

[TeePeeCreeper]

Does Transport require a noise test for every propeller or is it per type?

If it could be done once for a particular three blade propeller that would be replicated, it seems like a propeller manufacturer might have more to gain getting their products tested so we could just buy them certified. Thus spreading the cost over a few hundred units.

That’s a good question Beefitarian,

I’d be utterly gutted if I purchased an STC prop, installed it on my aircraft only to be told “up to you to obtain certification noise compliance”!

If it’s STC’ed an an approved mod why should further testing on the “owners dime” be required?

I am probably mistaken and will differ to PilotDAR for his insight.

Murky waters… uh I mean skies!

TPC

[photofly]

If it’s STC’ed an an approved mod why should further testing on the “owners dime” be required?

Read the thread title. This is about Serialized STC approvals. That's a custom STC created for one individual airframe at the owner's expense, for when a supplemental type certificate for the proposed modification doesn't already exist.

[PilotDAR]

Any prop or other modification which has STC approval is fine, TC won't be undoing existing STC's (it's too much work). It's the issue of a new STC or serialized STC approvals for props or other mods [possibly] affecting noise emitted by an airplane, which will be subject to noise scrutiny. Such scrutiny will be per propeller (or other mod) and airplane type (ie; if prop X is approved on a 182, it is not automatically approved on a 180 - separate test).

The only thing "new" this year is TC's actual application of the rules, they've been there for decades, and as I said, I dissented them when they were first introduced. It is an effort to harmonize with EASA and the FAA, and now it’s actually beginning to happen. I obtained STC approval two summers ago for a four blade MT prop to replace a three blade Hartzell. At the time, TC issued the STC with agreement about noise being complied with (without test), but the FAA are not issuing their STC for this mod easily, citing the change in number of blades. What was done by TC then would not happen now, the interpretation is more restrictive.

This broad application of the existing rules by TC staff cannot be called “wrong”, the rule is there, and has been for a while. However, as I predicted decades back, when I dissented this rule change to TC, it’s just creating an additional burden, and slowing a process, so as to discourage owners making changes to update, or renew their airplane. There are TC staff who are sympathetic to the problem, and effect on owner’s costs and practicality, and I’m working with them to find compromises – but it will never again be as easy to approve some of these changes…

[photofly]

Have the testing requirements for manufacturers seeking an STC for a new prop to market changed too? That's going to put up the price of, eg, an MT prop for a new type.

[PilotDAR]

I believe that the test procedures are recently unchanged, though I have not reviewed them in recent years. Prior to noise testing, I met with EASA noise specialists in Germany. They took time with me, and were very helpful. They offered me a soon to be approved (back then) new test procedure, which involved more overflights, but must less post test data analysis, and said it was more appropriate for GA planes than the test method at that time. They were right, and it worked out great. TC accepted the test method, because EASA recommended it. But, it was still a lot of work, and I have avoided invoking noise testing for any sSTC project since - just too costly to be worth it for one airplane.

But interpretations are becoming more ridged, and will impose the expectation of noise compliance/test for external changes for more than just propellers. I have a TC telecon this aft, where I hope to steer things away from massive oversight of all of these changes.

But, I remind readers here that the associations who represent airplane owners in Canada should be on this, reporting this evolving situation to members, and advocating for the minimum intrusion on the cost to maintain airplanes, consistent with continued safety. If owners have concerns about upcoming regulatory changes which could affect their maintenance of their planes, asking their associations would seem to be reasonable - it's what the associations are there for....

[photofly]

What is the post-processing required of raw noise data?

[PilotDAR]

For either the "original" EASA test method, or the "simplified" test method EASA proposed I use, the raw data must be "corrected" for various factors (I don't pretend to understand them). EASA explained to me that the original test method (four overflights) require extensive post data correction, which had embedded in the math, some penalties to assure conservatism of the final data. The simplified method EASA proposed to me required 36 overflights, but much less post processing. The 36 overflights were in groups of difference power settings and configurations, and produced a graph scatter of data, rather than just four points on the data graph. Therefore, the "scatter" of data gave much more confidence that the more raw data was actually representative, and they could accept it with much less conservatism.

For anyone who wants to research, the EASA/ICAO standard can be purchased (we did), its hundreds of pages!

[photofly]

I’m very interested in the details of the processing. Particularly, why it should be expensive. Four flights (for the simplified method) doesn’t seem that onerous, although I take your point about there being limits on acceptable winds.

[PilotDAR]

For those interested in getting into the depths of the methodology, ICAO's standard is here:

https://www.icao.int/environmental-prot ... .Vol.1.pdf

I learned this to the minimum required to complete the testing and reporting to produce an EASA accepted noise test on the 182 amphib, I don't pretend to understand all of it or the factors which affect the outcome or acceptability of a test.

[ruddersup?]

I always thought floatplanes did not have to have and meet noise testing. Guess this has changed.

[PilotDAR]

CAR 521.159(2)(b) permits an approved plane to be converted from or to skis or floats without further noise approval. However, the change of propeller to any configuration airplane brings noise compliance in as a requirement, which may require a noise test to satisfy.

[PilotDAR]

I had a computer meeting with six senior TC staff yesterday to work toward a solution yesterday. I was fairly heard, and said that I was speaking on behalf of my clients, private owners in GA. TC said that "the industry" should be approaching TC with the problem, as they would have more weight behind what they say, than just my single voice. I said that in terms of GA in Canada, it was much more a scattered gorup of owners, than an alphabet group. TC suggested COPA or GAMA might approach TC. I inquired about GAMA, as I don't think that GAMA much cares about aftermarket propeller changes on Canadian GA planes, the TC people saw my point. But, they left COPA on the table....

Maybe COPA would consider this recent reduction in available service to owners, worthy of their attention. I have spoken with my COPA Director about this. Maybe some readers here would too? What I see, which I anticipated twenty years ago when this all first started, is TC applying the regulations for "acoustical change" so literally, that any meaningful change to an airplane would require at least an analysis, or worse, a test, to demonstrate compliance. This will make prop change approvals on small legacy GA planes unaffordable.

It would help, if COPA members would speak to their COPA Directors, and indicate that they support TC issuing a "global exemption" applied "demonstration of compliance" for acoustical change for legacy GA airplanes, particularly for propeller or engine changes required for continued operation. TC's words, not mine. If COPA takes that to heart, and conveys that theme to TC Aircraft Certification persuasively, perhaps TC will relax their expectations of "demonstration of compliance" a little, and we DAR's can keep such changes affordable for owners.

The TC staff reminded me that "it is the law" (CAR 521.159) that acoustical change be considered when noise could ahve been affected by a design change, and they won't break the law by overlooking it. Yes, okay, I get it, we're not going to break the law about this, but what TC looks at, and how hard they look at a 40+ year old plane, which the owner just wants to keep flying, is open for some discussion.

In the mean time, as it stands now, if the new prop you desire is not STC'd on your airplane type, with the engine you have installed, a serialized STC will not be practically available for a diameter larger than what you plane presently allows, a different "type" (metal for composite), or more blades. And we did not get into engine power or exhaust changes. At this point, we're struggling through just how to approve a two blade metal for a two blade metal, of the same size.

This is one of those times (as it was about twenty years ago when discussion about noise regulation first drew a lot of industry silence), that those of us who provide approval services for GA planes could really use some support from "the industry", with TC....

[photofly]

Clark Morawetz.... pull your finger out!