Why Not Fuel Injected GA Aircraft 2

[MiketheEngineer]

Structural here that does a little flying once in a while and I have a question.

Every general aviation (GA) plane I have flown uses a carburetor. The pilot always has to worry about ice and the need for carburetor heat. If you read the accident reports - many are probably from carburetor ice. Typical scenario - dew point and temperature are close and pilot states "Engine suddenly quit when I pulled back on the power". Down he/she goes.

With fuel injection found on almost every auto engine - why is it not used on GA aircraft??

 

[dgapilot]

The field approval process isn't dead, but has detailed restrictions as listed in Order 8900.1 Volume 4 Chapter 9. Changes of the sort discussed here i.e. carburetor to fuel injection would at the very least require support from a DER, if it would even be considered for a field approval. As a one time STC, it would still require a fair amount of engineering that would include runs to verify cooling, power output, and relaibility. Most likely have to put the airplane in Experimental R&D to verify the design, then Experimental Show Compliance to verify compliance with all relavent regulations, then finally back to standard.

Just to move the paperwork thru the FAA ACO would take at least 6 months based on my experiance. The costs would be far more than the value added.

As for fuel injection in general aviation, Continental had the A-50-5J certified back in 1938. Continental had all the small engines from the 50 hp to the C-90 certified with fuel injection, and there is an STC to put fuel injection on the O-200. Problem is that the High, Excello, and American Bosch injectors weren't known for reliability.

 

[debodine]

I could use some updating here, as I have been out of the GA (General Aviation) world for about 20+ years. I have been commercial aircraft, FAR Part 25 for a long time now.

Please correct me if I err any where in my spiel below, and keep in mind I am only asking about GA right now:

The theory behind a field approval and an STC (Supplemental Type Certificate) is that the field approval and the STC require the same amount of research, testing, analysis and engineering design as the original manufacturer had to do to get the TC (Type Certificate), except that the field approval and the STC need only apply that rigor to the changes proposed, not to the unaffected portion of the aircraft and systems. Thus the airworthiness of the aircraft after a field approval or an STC is as thoroughly verified as it was when the aircraft was delivered by the manufacturer under the TC. (The STC can be applied to multiple aircraft, the field approval is a one-off approval).

So much for the theory. Now in the old days, the actual engineering, analysis, testing and research for a field approval or an STC typically did not approach the level of the manufacturer's efforts that resulted in the TC...in fact it rarely came close.

Fast forward to today...I get the impression that the research, analysis, engineering and testing for a field approval or an STC today in the GA world more closely approaches what the original manufacturer had to accomplish to get the TC.

So if I am correct, in the GA world the field approval and the STC process require more of what the theory says should be done. While I don't believe the field approval and STC yet match the level of effort for a TC, I do believe the FAA has demanded that the field approval and the STC come a lot closer to the original TC effort.

If I am wrong about the state of FAA approvals in the GA world of today as compared to decades ago, I look forward to being enlightened by my peers on this forum.

 

[dgapilot]

debodine,
You are close in your concept of how it is "supposed to" work. I think the real problem lies in the fragmented organization of the FAA. TC and STC projects go thru Aircraft Certification, and Field Approvals go through Flight Standards. Likewise, it all depends on what ACO or FSDO you have to submit your project to. Unfortunatly there is little standardization within the FAA when it comes to these types of projects. I've seen STCs issued that you scratch your head and wonder if any engineering was done, and I've seen Field Approvals that have a mountain of engineering data to support it and still have trouble getting it approved. Since Flight Standards came out with the Order 8900.1 referenced above, the field approval process seems to be better providing you can find an inspector willing to sign his name to it. I can't say the same for the STC process.

Overall, it shouldn't matter if it is a TC, STC, or Field Approval, the ame level of rigor should be applied. In the Field Approval, you may not have to produce the same level of documentation, but you still need to show compliance with the certification regulations. The regulations in questionar the certification basis of the original product, so if itwas originally certified under the CARs, you only need to show compliance to those older regulations (with a few exceptions)

 

[debodine]

dgapilot, thanks for the feedback. Regarding your last point about showing compliance, I understand what you are saying. Very often we are able to write our certification plans to show compliance to the FAR amendment levels applicable at the time of the aircraft manufacture/delivery. But as you correctly implied, sometimes the FAA will require a later amendment level regardless of the manufacture/delivery date. A good example would be flammability, and another would be emergency egress. Those are two areas where it is common for us to show compliance to later amendment levels.

I previously mentioned my background being commercial FAR Part 25 for the last 20 years. I work for an organization whose bread and butter is our ability to design major alterations. Our experience and attention to detail allows us to obtain FAA approvals with confidence and speed. Thus, I am not at all irritated when the FAA begins to demand that STC candidates must more closely approach the rigor applied by the original manufacturer, as that tends to move some of our less thorough competition out of our market. )

Having been out of GA for so long, I cannot say with certainty that such "tightening up" is really needed in the GA world or not.

I recall hearing early in my engineering career concerning designs that skirt the edges of compliance a statement from an "old hand" that such designs "...are perfectly safe until they fail...", usually followed by the old adage, "You get what you pay for."

Again thanks for catching me up to my old GA world.