Converting C-172 Flap System

Written by Steven Ells
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December 2015

Q: Hi Steve,

I own a 1966 Cessna 172G. I want to convert the flap system from electric to manual. Have you ever heard of anyone doing this? How can I do it?

I also want to install steps on the fuselage and wing strut so I can check the fuel level without having to carry around a ladder. What’s the best way to do that?

—Flap Man

A: Dear Flap Man,

I don’t know of any kit or approved modification to convert your 172G from an electrical flap actuation system to manual system. Cessna replaced the original manual flap system with the electrical system starting in 1965 with the 172F.

As you can see from the pages of the parts books (PAGE XX), the manual flap control system requires many more parts including brackets, pulleys, cables and the handle.

The flaps, extension rod and bell cranks are the same for both systems, but that’s the end of the compatibility.

There isn’t any STC for this change; however, since the parts and installation has already been done by the factory, you should be able to remove the electrical components of your 172G flap system and install the manual components of the 172F and earlier systems.

The key to converting back will depend largely on the willingness and abilities of your A&P mechanic to undertake the nuts and bolts of this task—and your luck in harvesting all the parts needed from a salvage yard that specializes in Cessna parts. (Longtime CFA supporters Wentworth Aircraft, Preferred Airparts and Dodson International are great places to start. See Resources for information. —Ed.)

There’s some doubt as to whether this change would constitute a major alteration. According to Appendix A of Part 43 titled “Major repairs, major alterations and preventive maintenance,” item (v) cites changes to the control system and item (ix) cites changes to hydraulic or electrical system actuation of components as being major alterations.

But there’s a question in my mind whether it is a major alteration. Are you really changing a control system with this change?

If you use exactly the same parts that make up the already-approved flap system installation of the 172F, I don’t believe that constitutes a major alteration since you aren’t really altering the flap system, you’re just installing a previously-approved system in place of another approved system.

But it doesn’t matter what I think. You or your mechanic will need to sound out someone at the local FAA FSDO for an official answer.

If they say it is a major alteration, the first step—before you buy any parts—would be to have your A&P prepare an FAA Form 337 and submit it to the FSDO to see the agency will sign off a field approval for this modification. (The link to download Form 337 can be found in Resources at the end of this column. —Ed.) Some FSDOs have the time and personnel available to sign off field approvals, and some don’t.

To answer your second question, I haven’t found any Cessna service kit or STC for the installation of fuselage- or wing-mounted fueling steps for the 172.

You’ve probably seen these steps on 150s and 182s, but I can’t find any approval for installing them on a 172. I suspect this issue here is the strength of the wing strut.

Sorry I don’t have any easy answers for you.

Happy flying.

 

Know your FAR/AIM and check with your mechanic before starting any work.

Steve Ells has been an A&P/IA for 43 years and is a commercial pilot with instrument and multi-engine ratings. Ells also loves utility and bush-style airplanes and operations. He’s a former tech rep and editor for Cessna Pilots Association and served as associate editor for AOPA Pilot until 2008. Ells is the owner of Ells Aviation (EllsAviation.com) and lives in Templeton, Calif. with his wife Audrey. Send questions and comments to .