Howdy folks,

I'm looking to remove what is essentially the carburetor heat cable on the C185. The series 100 Service Manual calls it the Induction Hot Air Control Cable. It operates the flap inside of the airbox that directs air from coming through the air filter or selects unfiltered air from inside of the cowling. I feel that this extra control is unnecessary and could potentially be another failure point since there is already a spring loaded door on the alternate air assembly. Plus the later model C185s do not have it. Plus it's one more thing on the panel. Plus I'll literally never use it since I fly an IO470 and not an O470.

Here is a photo of the device.


According to Part 43 Appendix A - Engine Major Alterations, my proposed modification is not:

“(i) Conversion of an aircraft engine from one approved model to another, involving any changes in compression ratio, propeller reduction gear, impeller gear ratios or the substitution of major engine parts which requires extensive rework and testing of the engine.
(ii) Changes to the engine by replacing aircraft engine structural parts with parts not supplied by the original manufacturer or parts not specifically approved by the Administrator.
(iii) Installation of an accessory which is not approved for the engine.
(iv) Removal of accessories that are listed as required equipment on the aircraft or engine specification.
(v) Installation of structural parts other than the type of parts approved for the installation.
(vi) Conversions of any sort for the purpose of using fuel of a rating or grade other than that listed in the engine specifications.”

Excerpt From: Federal Aviation Administration (FAA). “2019 FAR AMT.” Apple Books. https://books.apple.com/us/book/2019-fa ... 1424488813

I'm almost happy to call it a minor alteration. But since I'm probably wrong, how have you guys seen this done before?

When I read this post, I think:
You know it's major.
You want it to be minor.
You're hoping others here will call it minor to support your desire for it to be minor.

Yes, an IO has no need for carb heat. The engine conversion approval should have listed removal of carb heat IMO. But if it didn't, you can't.

14 CFR Part 43 Appendix A-A.1(xii) wrote:Changes to the basic design of the fuel, oil, cooling, heating, cabin pressurization, electrical, hydraulic, de-icing, or exhaust systems.

Removal of carburetor heat would change the basic design of the aircraft's heating system.

But this doesnt seem like a difficult thing to get approved on a 337.

I'm looking to remove what is essentially the carburetor heat cable on the C185.

It's not "essentially carb heat". That sounds like something a PPL student would describe alternate air as to another less experienced PPL student. It's being pulled from a different place, going to a different place, and is used to address a different problem.

Plus I'll literally never use it since I fly an IO470 and not an O470.

The only reason you would ever use it is precisely because you "fly" an injected engine.


Seems like your finding the most difficult solutions to a problem that doesn't exist, even though I agree that most people, especially fair weather flyers, will go their whole life never pulling alternate air.

asa wrote:

I'm looking to remove what is essentially the carburetor heat cable on the C185.

It's not "essentially carb heat". That sounds like something a PPL student would describe alternate air as to another less experienced PPL student. It's being pulled from a different place, going to a different place, and is used to address a different problem.

Plus I'll literally never use it since I fly an IO470 and not an O470.

The only reason you would ever use it is precisely because you "fly" an injected engine.


Seems like your finding the most difficult solutions to a problem that doesn't exist, even though I agree that most people, especially fair weather flyers, will go their whole life never pulling alternate air.

In that case, I misread. I thought he had Carb Heat AND Alternate Air.
Either way, you can't remove it as a minor.

I'll try to explain what I am trying to do using the IPC. S/N 185-0001 - S/N 18501832 all used a similar induction air box setup. All of these aircraft were equipped with an alternate air source that was automatically actuated through the use of springs. The major difference in airbox design of these aircraft was that S/N 185-0001 - S/N 185-1300 had a secondary cable actuated flapper valve inside of the airbox. Once the pilot noticed a change in manifold pressure, he could pull the control for the alternate air which would then cause the engine's vacuum to open the springs on the alternate air assembly which would then allow unducted air to enter into the engine's induction system. S/N 185-1301 and on used only the alternate air assembly to combat impact ice and other air filter blockages. This change removed the control cable from the cockpit and eliminated something else that could break.

All this being said, I would like to remove the valve that is located inside of the airbox assembly (#16) and the arm (#4). After this is all said and done, I would have a similar airbox setup as C185s S/N 185-1301 through S/N 185-1479.





I'm sorry if I ruffled your feathers for calling the cable a carburetor heat cable @Asa. You and I both know that's not what the thing is.

You are duplicating/copying the Cessna design used on later s/n's. That should not be difficult to approve at all. I have done this several times. For example, factory extended baggage on an early bird. Fuel tank with dual outlets on an early plane to replace the single outlets, etc

C180_guy wrote:You are duplicating/copying the Cessna design used on later s/n's. That should not be difficult to approve at all. I have done this several times. For example, factory extended baggage on an early bird. Fuel tank with dual outlets on an early plane to replace the single outlets, etc

For you past approvals, did you have to spend time with a DER / or the Aircraft Certification Office? Would I be right to assume that since these changes are already approved for a similar make and model, an ASI should be able to sign block 3 by reviewing data only?

No DER, no ACO. I showed them a copy of the IPC.

C180_guy wrote:No DER, no ACO. I showed them a copy of the IPC.

Almost too easy. Thanks!

C180 GUY, Do you think this method of approval would work for installing 1963 172 wider span horizontal tail surfaces on a 1960 172?