Carb to FI: Do I need Phase I Again

[lr172]

Ok, I read the recommended post. Here is the key language of Major (i.e. not minor) change:

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).


The only category that seems applicable is "Reliability," as the engine and plane should perform the same as before the change (W&B should not be considered appreciable as it will only be a couple of pounds). I don't see how the FI could be considered a reliability change. 10 of 1,000's of Lycoming engines have proven a pretty similar reliability track record for both. I can't imagine that changing from one sub-version of MA 4SPA to another would be any more major of a change than a change from carb to FI. The engine fundamentally performs the same either way. I could argue that changing to a different heat range spark plug is no less major than going from a proven carb to a proven FI (I will be using the tried and true Bendix setup).

I guess my real question is, does my interpretation count for anything.

Larry

[Bill Palmer]

Hi Larry,

Please check your PMs or email.

[rvbuilder2002]

Originally Posted by lr172

I guess my real question is, does my interpretation count for anything.
Larry

In reality, it is the only one that counts (as long as there was no incident that resulted in an investigation in the first few flight hrs after the modification).

You will be the one doing the work and I presume doing the return to service log book entry. So you hold the responsibility of deciding whether just doing a short post work test flight meets the requirements of your operating limitations based on the FAA's definition of a major change.

It sounds like you have made that decision.

[Canadian_JOY]

If one takes a few minutes to peruse the Experimental Aircraft accident history, one will find a large proportion of accidents have happened in the "new airplane" phase. Further investigation will reveal that, of these "new airplane" accidents, a startling proportion of the airplanes came to grief as a result of fuel delivery problems.

With this in mind, irrespective of regulatory requirements, the number one driving factor here has to be flight safety. Changing the fuel delivery system will mean changing a large number of components in the fuel delivery chain. Any one of the new components could introduce a flaw which ultimately would result in engine stoppage. From this perspective, it would seem prudent to voluntarily enter a formal flight test regime, with the usual limitations on passenger carrying and distance from home field. Whether this is formally documented as a return to Phase 1 or not can be debated until the cows come home - your grieving family won't care about the regulations. The only thing that really matters is that you ensure your safety and the safety of others isn't compromised.

With respect to the wording of the regulation, installation of fuel injection will require the removal of a cockpit control (carb heat) and perhaps installation of new cockpit controls, plus introduction of new procedures for starting, running and re-starting the engine. One could easily and logically argue this modification materially changes the operational characteristics of the aircraft.

If going to Fuel Injection, don't forget to update your POH and checklists to reflect the new procedures for engine start / shutdown, restart, etc.

Above all, make sure you test to ensure you have full fuel flow to the engine under worst-case conditions... before you run the engine for the first time. It's amazing how easy it is to introduce a little piece of "gunk" into the fuel system when so many components are being swapped.

[Mel]

Very good post Mark. I agree wholeheartedly.

[lr172]

Thanks for the insight and cautions here. My goal was not to minimize testing. I recognize that I am changing a lot of components here and a good deal of diligence is required to be sure that I got it right and that the components work, including a few different flights with ground checks between them, just as in my initial flights. Clearly I wouldn't carry passengers until I was comfortable that the system was performing well across a variety of scenarios and I had given it some time to settle in and expose it's flaw. I just didn't know if I needed the rigor of the formal Phase I and the FSDO contacts. After all this, I may end up spending 5 hours getting comfortable with the performance and having given this more thought will likely just do the the Phase I testing and document it that way.

Larry

[lr172]

Originally Posted by Canadian_JOY

With respect to the wording of the regulation, installation of fuel injection will require the removal of a cockpit control (carb heat) and perhaps installation of new cockpit controls, plus introduction of new procedures for starting, running and re-starting the engine. One could easily and logically argue this modification materially changes the operational characteristics of the aircraft.

This raises an interesting point for me. I plan to fly this plane IFR someday and was considering leaving the carb heat setup after the conversion. My thought was that it could potentially eliminate or reduce water or even ice build up on the air filter when flying in rain. Is there a downside to this approach? I do have an alternate air door to overcome a clogged filter.

[rvbuilder2002]

Originally Posted by Mel

Very good post Mark. I agree wholeheartedly.

As do I, which is why my opinion is to treat it as a major modification.

[Mel]

Originally Posted by lr172

This raises an interesting point for me. I plan to fly this plane IFR someday and was considering leaving the carb heat setup after the conversion. My thought was that it could potentially eliminate or reduce water or even ice build up on the air filter when flying in rain. Is there a downside to this approach? I do have an alternate air door to overcome a clogged filter.

Leaving the carb heat set-up in tact will NOT cause a problem. As a matter of fact, induction icing is not unheard of with fuel injection. It is rare, but it does happen.

[Gisnar]

I converted my 0-320 to fuel injection. I was required to go back into phase one for 10 hours by local FSDO. When asked why they were very reasonable and produced the data. They had had several major problems with the conversion and were just trying to be safe. No arguments with that