Prop Change: Major Alteration or Not?

RV8R999 · #1 01-12-2012, 08:39 AM

Looking for opinions
Does switching from a FP 2-blade Wood Prop to a FP 3-Blade composite Prop constitute major alteration?

FAR 21.9 (I think) defines a major alertation as any change which changes the operating characteristics.

While performance may (or may not) change the operation (pilot actions) will not.

Curious what ya'll think?

flyingriki · #2 01-12-2012, 08:52 AM

Quote:

Originally Posted by RV8R999

Looking for opinions
Does switching from a FP 2-blade Wood Prop to a FP 3-Blade composite Prop constitute major alteration?

FAR 21.9 (I think) defines a major alertation as any change which changes the operating characteristics.

While performance may (or may not) change the operation (pilot actions) will not.

Curious what ya'll think?

Absolutely! I didn't know (exact same prop change from 2 blade wood to Catto 3 blade) and had to confess to my FSDO a couple years later. He scolded me and let me sign it off with a reference to him in my log. Worst part, in my mind, was an A&P/IA had made the change and never mentioned this requirement. But then he left a lot of problems......

vic syracuse · #3 01-12-2012, 08:56 AM

Yes, this is considered a major change and will require some time back into Phase I. Think about major changes as those that have the potential to affect the FLIGHT characteristics of the airplane.

Vic

billgill · #4 01-12-2012, 10:42 AM

a major alteration.

We had an RV-4 on the field that changed from a 2-blade wood prop to a 2-blade metal prop. The IA that did the work called his PMI at KC FSDO and he was told that this was NOT a major alteration considering that both props are fixed pitch. I'm sure one would get differing responses from different FSDO's.

Bill
RV-7 N151WP
Lees Summit, MO

LifeofReiley · #5 01-12-2012, 11:14 AM

Quote:

Originally Posted by billgill

a major alteration.

We had an RV-4 on the field that changed from a 2-blade wood prop to a 2-blade metal prop. The IA that did the work called his PMI at KC FSDO and he was told that this was NOT a major alteration considering that both props are fixed pitch. I'm sure one would get differing responses from different FSDO's.

Bill
RV-7 N151WP
Lees Summit, MO

Exactly... this subject has been beaten to death before, really depends on who you ask @ the FAA. You WILL get different answers.

Toobuilder · #6 01-12-2012, 01:42 PM

I can see where the FSDO would give differing opinions. You're looking for pilot/vehicle interface issues (none here), flight characteristics (doubt it) and W&B (maybe).

I could go either way, but would lean towards no if the weight change stayed within the CG envelope.

Bob Axsom · #7 01-12-2012, 02:03 PM

If you carved your own original design and implemented some inflight pitch change mechanism... But an off the shelf prop proven compatible with the engine and airframe I don't even see as in the gray area of the rules. If you built the plane and have your repairman certificate you need to read the rules and implement them in a sensible way as they are written, document everything as required and move on.

Bob Axsom

vic syracuse · #8 01-12-2012, 02:55 PM

Here we go again with opinions. The rules are pretty specific, actually, even though different FSDO's and A&P's/IA's seem to interpret them differently. Bob, given that all of our Experimental airplanes are "hand-made" to no specific certification process, there is no basis to say that one propeller is proven on many airframes. Almost everyone one that I inspect has it's own differences and nuances, and we all see this evidenced by the numerous cooling issue posts by builders on this site alone supposedly with the same airframe/propeller/cooler combinations. To think that a change from a 2-blade to a 3 blade will not cause some differences in flight characteristics and/or engine operating parameters is not true.
I certainly wouldn't make this type of change without doing some testing and comparing, and I would question why someone else wouldn't want to do the same. Even at the cost of fuel today, 5 hours of flight testing is miniscule in the scheme of things and could probably be accomplished over a week end.
My .02.

vIC

Toobuilder · #9 01-12-2012, 04:27 PM

Quote:

Originally Posted by vic syracuse

Here we go again with opinions. The rules are pretty specific, actually...

Not to be argumentative Vic, but isn't your statement that the "...rules are pretty specific..." itself an opinion? After all, I'm an A&P, have read the regs, and like many other certified mechanics, FSDO personnel and other generally smart people, come to a different conclusion. Without trying to establish which side is right or wrong, doesn't that at least indicate the rules are NOT specific?

Can you provide the language in the reg that clears this all up? If I missed it I will gladly stand corrected.

RV8R999 · #10 01-12-2012, 04:36 PM

According to our OpLims this is the rule:

21.93 Classification of changes in type design.

top
(a) In addition to changes in type design specified in paragraph (b) of this section, changes in type design are classified as minor and major. A ?minor change? is one that has no appreciable effect on the weight, balance, structural strength, reliability, operational characteristics, or other characteristics affecting the airworthiness of the product. All other changes are ?major changes? (except as provided in paragraph (b) of this section).

It isn't at all specific. The word appreciable is open for interpretation....

I'll call my FSDO tomorrow.