The International Cessna^® 170 Association

When you consider modifying your airplane with STC's, it's a consideration to look at what associated equipment you might be limited to as well.

I rec'd this question from the cyberspace:

I am trying to find a replacement prop for a c170B with a Doine conversion and an O-340 lycoming. It currently has an HC-82VK-D/V8433-12 subject to a recurring AD. The customer wants the one that is not subject to the Ad, but no one seems to be able to tell me what that is . Can you help??

I hated to remind him that when STC's are applied to aircraft, only the equipment approved in that STC is applicable. My answer:

There's a problem with engine conversions (and other STC's). They are approved only as they were originally submitted/approved or subsequently modified/approved.

If you have a Doyne engine conversion then only the prop(s) certified for that conversion is legal... ...unless you or someone is willing to go to the trouble and expense of re-certification.

In other words, unless the prop is already approved for the Doyne STC... then no other prop is allowed without a further basis-of-approval. Since STC's are a fairly small and proprietary market, prop mfr's are unlikely to go to all the trouble to get their other props certified/approved for such limited applications.

Sorry. If the prop manufacturers and Doyne cannot help you, .... I have no other answer.

Anyone out there have knowlege of a different prop approved for this airplane with the Doyne STC?

I would ask Hartzell for a recommendation on a replacement propeller and ask their technical department to provide a letter noting he differences between the two propellers. The reality is that the manufacturers newer propellers are superior to their previous offerings.I would then approach the FAA, present them with the recommendation and the technical data on the two props and see whether a 337 could be used for your situation. Getting the regulatory bodies to acknowledge that could be difficult. I have a 337 for my 0-320 Doyn conversion that switched from the steel hub to the compact Alum hub and yes it was issued years ago. I'm thinking of upgrading my propeller as well but as I just overhauled the prop I'll guess I'll be swinging it for awhile.

Oh and everything George mentioned is right on the money with respect to finding part replacement when you go down the STC road.

The very few Doyne conversions that I know of have changed the prop, put a spinner on and go flying. It doesn't seem to bother their A&P,IA or the local FUZZ. However, it's very possible none of them know about the AD.

Prop's Suck!
Working with two friends (that alwayse costs) and my principal at the FSDO I spent over $600.00 of my time, that I ate. to get their aircraft legal! Someone had hung a prop (with no log entry) I knew that It was good but the paper work wasn't . And the Principal knew it to! (He said A LOT OF WORK FOR A FIFTY YEAR OLD AIRCRAFT ISN'T IT!) When it was said and done, I lost all my time and made the owners buy a $200.00 STC, which makes everything OK!!! And Life goes ON!!!!!!!!
brad