Not trying to be confrontational about this, but what part seems like a major alteration, according to the FAR definition of major alteration?


And the smoking airplanes kit comes with a checklist for continued airworthiness (for any future IA annual), and has a momentary switch for performances that is to be used during any low level flying, per the instructions. You lift your finger, and the pump stops pumping.


During my research, there were a lot of old wives tales about someone's brother's neighbor's sister in-law having a run in with the FAA about their smoke system, but no one had direct interaction with a fed that said it wasn't a minor alteration. There were a couple IA's that stood on their conviction that it was, without any substantiation.

Since you mention Smoking Airplanes. Their website says it is a Major Alteration and they give sample 337s for basis of field approval.

https://www.aircraftspruce.com/document ... nesFAQ.pdf

https://smokingairplanes.com/pages/faa-337

https://cdn.shopify.com/s/files/1/0098/ ... 1733528158

Supplemental Type Certificate (STC)
The FAA requires that a STC be specific to a particular aircraft make and model. Given the number of different aircraft types world-wide it's not practical for Smoking Airplanes to obtain a STC for all aircraft make and models.

Field approval for smoke systems are completed via the FAA 337 form (USA). Please check with your local aviation authority if not in the USA. An Inspection Authorized Airframe and Power Plant mechanic can prepare the 337 form for your aircraft. You may view examples of completed 337 forms on our website here:

https://smokingairplanes.com/pages/faa-337

A door steward and Rosen sunvisors also have STC's, even though they are really minor mods. People do field approvals for things all the time that aren't needed. Again, would love to be shown the basis for a major mod via the regs or advisory circular.


Also, smoking airplanes doesn't say it's a major mod. They just give examples of 337's and the reason for them to not go for an STC (also, the faa specifically says they won't issue an STC for a minor mod...)

Appendix A to Part 43—Major Alterations, Major Repairs, and Preventive Maintenance

(a) Major alterations—(1) Airframe major alterations. Alterations of the following parts and alterations of the following types, when not listed in the aircraft specifications issued by the FAA, are airframe major alterations:

(i) Wings.

(ii) Tail surfaces.

(iii) Fuselage.

(iv) Engine mounts.

(v) Control system.

(vi) Landing gear.

(vii) Hull or floats.

(viii) Elements of an airframe including spars, ribs, fittings, shock absorbers, bracing, cowling, fairings, and balance weights.

(ix) Hydraulic and electrical actuating system of components.

(x) Rotor blades.

(xi) Changes to the empty weight or empty balance which result in an increase in the maximum certificated weight or center of gravity limits of the aircraft.

(xii) Changes to the basic design of the fuel, oil, cooling, heating, cabin pressurization, electrical, hydraulic, de-icing, or exhaust systems.

(xiii) Changes to the wing or to fixed or movable control surfaces which affect flutter and vibration characteristics.

It really comes down to your IA. If he doesn't see the installation of a smoke system as a major, then you're fine. He is the one involved with the yearly annual, not everyone else on the internet.

If you seek unanimous approval, don't show your hand.

At the end of the day, I think it is a major. You are adding a full electrical circuit, firewall penetrations, flex hose installation, exhaust modification, and a change to the weight and balance that has to be factored as an EW increase and any potential CG shift between smoke empty and full.

When done correctly and well, its no big deal. But why document something controversial as a minor if it is going to become a sticking point for every other IA down the line.

Plus for an aerobatic airplane like originally stated how can you show the tank installation will be ok positive and negative G without some type of pull test or engineering data.


For future IAs to inspect. What are they inspecting? The installation has no data to see if it conforms to what was determined by a previous IA to be a minor alteration.

Oddly enough I pay .1 hr each Phase for the Rosen visor STC ICA to be complied with on the Kingair. I'll admit that STC is a little silly to have but they may have needed it for installations in airplanes with government contracts. OAS inspections for fire and forestry work. etc.

Door Steward installation required drilling multiple holes the door and fuselage structural door lower channel for riveting on the attach brackets. Original door opening limiters were removed in some cases. Yes STC was needed. Deviates from the original parts book and so they give the new installation and approved data.

A Smoke system with electrical changes, plumbing, pump, tank installation, venting, firewall penetrations, exhaust system modifications, in the cockpit has a lot of parts. It's fine if your IA is ok with it. But down the road what makes the next IA or repair station performing Annuals accept it as a minor or does it pass as a minor in all FSDOs with typical ASI looking?
If the airplane goes for a checkride does the DPE accept it as minor during the log or systems review?

This is the trouble with the FAA. There is no consistency or specific legal ruling printed that I can find.

I don't anticipate changing a couple of the guys in this thread from their stance, but below is the definition of a major alteration and how a smoke system doesn't fit it. Remember, anything that doesn't qualify as a major alteration is by definition, a minor mod.



An install includes adding an electric load and affixing the tank to the aircraft. both actions use elementary skills. Same as adding an EGT indicator or USB charging plug.

All this to say, a lot of aviation enthusiast tend to make a mountain out of a mole hill. If an alteration can be made and substantiated as a minor alteration, efforts should be taken to do so. no reason to make things harder than they need to be. A discussion should be had with your IA, who signs the annual. Most are receptive once you go down the above list with them. For those that aren't, I guess you can still get an annual and have it squawked as a discrepancy, then signed back off from your A&P. But I would be looking for a new IA if that were the case...

"........... but no one had direct interaction with a fed that said it wasn't a minor alteration. There were a couple IA's that stood on their conviction that it was, without any substantiation."

My previous post in this thread was about a group of T-6 owners who had installed smoke systems after being told by a retired airline engineer that it was minor. So five did.

To alleviate the situation at annual inspection time, I was in contact with a FSDO PMI in OKC who was willing to coach me thru the process and add his help. This FAA guy is very knowledgeable and helpful. He is an active pilot and RV homebuilder.

He instructed me to first inactivate the systems while we gained approval. He than consulted with his ACO and I sent the Form 337's to him. AC 43-210A has the flow charts labeled Figure 3-1 and figure 3-2 to help with the decision making. of whether being a Major or Minor alteration.

My view, one is installing an extra tank of some gallons of flammable liquid in the airframe. pumping it by some method and injecting it into the heated exhaust system. What could go wrong?

P.S each of the T-6's have Standard airworthiness certificates.

A Fed told them it was a major, or you under your IA told them it was a major at annual?


Literally thousand of planes flying around with smoke systems. Not too many exploding because of the "flammable liquid" inside the cockpit (as Doug mentioned earlier, combustible but not flamable).

https://yesteryearaviation.com/smoke-system

https://www.fs.usda.gov/eng/pubs/pdfimage/63571302.pdf

https://www.airresearch.com/features/st ... ders/66584

It's interesting even crop dusters had an STC for installing smoke systems.

https://static.wixstatic.com/media/a27d ... 9b~mv2.jpg

American Champion take on it.
Engineer
Dec 27, 2019

American Champion recommends the 3.5 or 5.5 gallon Smoking Airplanes system, smokingairplanes.com. We typically install the 5.5 gallon vertical tank (P/N A-SA-SFO12V) but the other tank options should work as well. Installation is via a field approval. The tank rails are mounted to the floorboard in the baggage area; fasteners at the front of the floorboard are replaced with bolts and AN970 washers. If you are looking for a smoke system with an approval consider Milman STC SA874NW.

Charlie,

We went down this road earlier in the thread. Rosen sun visors has an STC. Doesn't mean its a major. Plenty of wrongly filed 337's on planes for other minor mods. Doesn't mean they were right.


The FARs are clear. Either it fits the list in appendix A of part 43 as a major, or its a minor. I've proven my side as a minor by going through that list item by item. Someone who claims major needs to prove it by showing what item it alters in a major way from appendix A of part 43.

OK you win... I'll keep doing it my way.

You can do the same.

I'll leave you with info for determining the tank mounting and strap required strength. Unlimited aerobatic airplane should have some thought put into the mounting and tank design.


https://www.faa.gov/documentlibrary/med ... .13-2b.pdf