Periodic Legacy (A) Airframe Inspection

General
1

It seems that Sonex do not publish/pdf a periodic airframe service/inspection manual.

Such a manual would containe, in addition to generic advice, targeted information based on historic / know problem areas.

Only Sonex would have access to the historic data. So only Sonex can come up with a aircraft specific service manual.

I note that this topic has been around since at least 2015 - Sonex has not addressed the matter.

Sonex advise is to use one of the available generic (no aircraft specific) advisories eg Appendix D of FAR part 43 or CASA schedule 5, etc.

My engine & propeller have detailed periodic service/inspection manuals - the airframe should have the same. Not good enough Sonex.
:smiling_face_with_horns:

2

It seems that would be a good idea. Just to play devil’s advocate, I would think that although Sonex could issue advice on some of the major inspection points that are things that still come up - like the gear leg bolts, etc., but as the builder, I should be able create a fairly exhaustive list of inspection items on my own.

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3

I did, and I’ll share it when I get a chance.

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4

Hi Kevin,

“…things that still come up - like the gear leg bolts, etc”
This is addressed by the Service Bulletin system. Nothing about an aircraft is static ie revision/updates are expected/the norm.

“…as the builder, I should be able create a fairly exhaustive list of inspection items on my own.”
Sure you can make your own inspection schedule. Unfortunatly it will be just your best guess.
Only Sonex will have fleet (all aircraft ) historic data , which will enable a targeted maintenance/inspection schedule to be created. :smiling_face_with_horns:

5

Sonex does not have my data.

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6

Like many others, I use Jeff Shultz’s checklist with modifications for my airplane: Sonex Condition Inspection Checklist

I think your suggestion makes sense, in principle, but what sort of problem areas do you have in mind? After going through a checklist like Jeff’s, I’m not really sure what problem areas are left?

Here are some of my own personal priority areas from personal experience:

I’ve had issues with some of the holes on the main landing gear wallowing out early on likely due to poor assembly and not shimming the legs in the sockets. This was solved by welding and re-drilling the holes, but I pay more attention now. I feel like I could still check the bolts that have broken for others more often than I do. I wish we understood that issue better. Tailwheel assembly and pushrod also seems like a spot that could take some wear, but it’s also easy to inspect every flight.

Around 10 years the pads on my mechanical brakes disintegrated and had to be replaced. I never reported this to Sonex and I don’t know if it’s a common issue or one I could have noticed during condition inspections.

I try to keep an eye on the throttle cable since many years ago I heard of it breaking for someone, but mine seems as good as the day I installed it.

One time, I pinched the cork gaskets when installing the valve cover and ended up with a significant oil leak. I stopped using cork pads and switched to reusable fiberglass reinforced silicone.

My ELT antenna base broke due to UV exposure.

Chose to replace the windshield due to scratches from dust and cleaning over the years along with yellowing due to UV.

Haven’t had any issues with my Teflon fuel lines :slight_smile:

Voltage regulator is just fine. Replaced the Odyssey battery once. It may have been fine, but it was hard to start a couple times over the winter. Really should have a trickle charger or at least an easy way to charge the plane during preflight.

The SB about the alternator screws being too short came out around the time I finished the airplane. I had to replace the screws and was VERY careful to clean them and apply the right loctite primer, etc. So, I should be fine. Despite all this, I pay a lot of attention to the charging voltage, but there isn’t an easy way to check the screws on a schedule.

Had to replace all coils of the Aerovee ignition system at least once. This is an obvious place where a schedule could help, but I don’t know there’s anything to check for on a schedule.

It’s important to keep on top of valve adjustments, etc., with the Aerovee, but that schedule is provided in the engine manual. Also probably a good idea to monitor compression–I do it with the ignitions off by turning the propeller by hand after flying.

I just realized you are mainly concerned here with airframe specific inspection. I’m always so focused on the engine :slight_smile:

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7

Do other plans / kit mfrs publish inspection books ?
Seems like much of the variation and issues with experimental home built airplanes has more to do with the original construction and maintenance and up keep by the owner / operators. Unless they physically inspected each themselves, it would seem many things would be a laundry list of “we heard of this once and we heard of that once”. IF they learn of things that happened and can solidly trace them back to design / kit quality related, then they can ( and do) issue SBs. Even those are an optional in the experimental world… best practice, but optional none the less.

While this is more slanted toward RVs, this book may be of interest ( I have a copy) as it is a collection of things that Vic Syracuse has seen as an A&P and DAR of airplanes he has inspected.

most of what Vic has in this book are a collections of failure of “us” as builders / owners / maintainers of these great flying machines…

The learnings and sharings come from forums like this and the openness and willingness of the people that frequent here. And they are invaluable!

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8

Here’s my template. Note that the extra credit items are for projects that I want to complete during annual.

Waiex annual template 2026.xlsx (14.2 KB)

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9

Given that a Sonex builder has the choice of many engines & propellers, I don’t think it should be up to Sonex to supply the engine/propeller service manuals.

I already have access to all of the Rotax 912ULS manuals and the service manual for my Airmaster propeller.

The airframe is another matter. Yes each Sonex, may have some degree of customisation, however the basic airframe, control systems, undercarriage, etc is Sonex through & through.

I contend that Sonex is in the best position to make available (pdf) a periodic airframe service manual incorporating all the problem areas (if any) that customers have informed them of over time. That they have not done this, suggests a level of indifference to their customers (pilot/builders) :smiling_face_with_horns:

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While I see value in your premise and proposal, I disagree with the last sentence of your conclusion

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11

Here’s my inspection checklist to share.

Sonex Serial Number 1102 Maintenance Schedule Check List.pdf (54.2 KB)

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12

I asked the factory about this years ago. They said inspect it like any other EAB or light aircraft and I agree with that.

Suggesting this indicates something isn’t an accurate representation of what many of us know and love about Sonex.

I’ve had my differences with them over the years but they are good folks who care about us. I’m always looking here for more information about potential problems, but that’s another thing I love about it.

Us.

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13

The underlying assumptions of this statement are false.
The first assumption hiding behind “ that customers have informed them of” is that self reporting provides good information. Self reporting, at best, is unreliable, and fraught with bias. Understanding the Limitations of SelfReported Data - Insight7 - Call Analytics & AI Coaching for Customer Teams . (over-view)

Another assumption is that the staff at Sonex have both the skills and the time to gather the data. Writing the code to extract the information from multiple sources and compile it into useful data and make it readily available can run thousands of lines of code. (I have personally written code that went to 3,700 lines) I doubt that the staff at Sonex have the specific coding skill set required to create the report.

Data mining requires a deep dive into the data. The first part requires data modeling, identifying errors in the data, (i.e. text in a numeric field) and either modifying or deleting the errors, etc., etc. All of this can take months.

So ,after hiring a data scientist for a 3 to 6 month project, they end up with a document of questionable significance which creates a potential to create a significant legal liability.

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14

You might have answered your own question here.

Your airframe has wing tanks, a homemade header tank, homemade dialatrim wheel, although it is very elegant and functions similar to the Sonex one. Your wing incidence has been changed and not sure if the stabilizer was changed to suit. Nonstandard wheel axles and brakes and perhaps some other major changes. I am also envious of your constant speed propeller.

This is just one example of builders departing from the plans and I am also guilty of doing this and I don’t think a standard Sonex maintenance program would be much use to many of us without modifying that too.

I use the Rotax 100 checklist for the engine and I modified the Jeff Schults form to suit my aircraft and also made sure that there was nothing in CASA schedule 5 that wasn’t covered as I am signing off stating the following:

*“I certify that this aircraft has been inspected on ________ in accordance with the scope and detail of Casa Schedule 5 and was found to be in a condition for safe operation.

Signed __________, Repairman # __________ “

Not sure where I read it, but the above statement needs to be signed off in the logs and maintenance forms in Australia.

Hope this helps

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15

Thank you for your check list. I will take from it what applies to my aircraft. Thanks again :smiling_face_with_horns:

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16

Your opening statement “I asked the factory about this years ago.” supports my position.
Sonex have been approached, over many years, to come up with a periodic airframe inspection/service document and have not done so.
The only conclusion is that they are indifferent to the concerns of their customers, if not in general, certainly on this point :smiling_face_with_horns:

17

“The underlying assumptions of this statement are false.”
I put it to you:
Given that inspection/maintenance schedules of any machine, are derived from large data sets (experince) it is reasonable to assume that the entity with the most data (Sonex), will deliver the most efficacies manual.
Its unlikly that there are entities that own a significant fleet of Sonex aircraft, from which to draw up an effective periodic airframe service/inspection document.
Without access to the largest available (no matter how limited) data set, individual owners can only rely on their own (highly variable) experince, like aircraft service documents and generic documents - hardly the best situaton.
The excuses you list, for not supplying, what every other aircraft company, I have dealt with, delivers on (in detail) are just that, a list of unacceptable excuses for a company that has been in existence for near 30 years.
A periodic airframe service/inspection document should have been commenced, by Sonex, in the early days of the companies existence. Naturally such a document would have been subject to refinement and review over time. By now we (the customer) would be accessing such a document on line (and/or as part of the construction plans) as a normal part of the Sonex after market service.
To summarise the above argument - Sonex is “slack” :smiling_face_with_horns:

19

It seems they are indifferent to one customer. Maybe indifferent is not fair, but there is not much payback considering the rest of us seem happy making checklists based on Appendix D of FAR part 43, and sharing in the community.

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20

here is what Van’s Aircraft provides:

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21

Another more likely conclusion is that it’s not standard practice for kit manufactures to provide this due to builder modifications or liability concerns. From Yearly Condition Inspection, Part I - KITPLANES :
“Most kit manufacturers do not provide condition inspection checklists to their customers, arguably because every plane is different to some extent. Liability concerns also undoubtedly play a part.”

There aren’t a ton of manufacturer created conditional inspection checklists out there among major kit manufactures with the exception of E-LSAs which are required to be built exactly to plans. I don’t think it’s fair to say all those companies are indifferent to concerns of their customers.

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