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[phatairflyer]

Hello all, i am new to this site..I live in Louisiana, and currently have a Piper Tomahawk that i am getting ready to sell so that i can purchase and transition to a LSA. I am looking at several different aircraft for sale, It will be just me and my wife that want to have something for weekend or weekday flights (i am retired) and will be asking questions about some of the planes for sale. My first choices i am leaning towards is a Zenith 601 series or 650 I have read lots of stuff about the wings and the mods that are available..but i am wondering are the failures that have happened due to bad building, design or overstressing the aircraft. If i purchase one without the mods that has a few hundred hours on it..why would it all of a sudden not be safe?. If i can afford it i am also looking at Arion Lightning, and if i have to really budget myself..I have always like the ercoupes..a timeless design that while not the streamlined modern looking airplane in the world..they have a certain class to them. So i am going to have to get my LSA license..i currently do not have any license..i will be looking at instruction for my certificate. I did get about 45 hrs in a Piper Colt back in 1971 went into the Army and never took my checkride. Since then i flew hanggliders for many years and then lots of years in Ultralights and accumulated about 650 hrs of Ultralight time..none of which applies to anything..but i am not a new pilot so to speak. Currently taking my online Gleim ground school course. Thanks all..glad to be a part of this forum. Take care, have a great weekend and safe flying!

[Sling 2 Pilot]

How did you wind up with the Tomahawk?

[JimParker256]

Sorry this is so long, but it's important, and I didn't want to give your question an overly simplistic answer...

Pertaining to the Zenith 601/650 (virtually identical airplanes structurally), AOPA published a blog article that you might want to read before deciding to fly an un-modified one "as is"... Here's a link to the article: AOPA Blog. Be sure you follow the link in that article to the FAA's Special Airworthiness Information Bulletin on that topic and read it as well. It's rather eye-opening! The key finding (for me at least) was that the designer did not meet the ASTM design standards when it came to wing loading. The FAA found issues with flutter, stick force gradients, airspeed calibration, and with the operating limitations.

So, you asked whether "the failures that have happened [were] due to bad building, design or overstressing the aircraft?" The "root cause" appears to have been poor design, which was then amplified because pilots were inadvertently (and perhaps sometimes knowingly?) overstressing the airplane. Some of this was caused by the stick force gradient problem, potentially compounded by flying very close to the published limitations of the airframe. Though some were likely caused by the pilot flat-out ignoring the limits because "pilot excuse"... (I can fly aerobatics in this airplane – I'm just that good!)

The FAA felt (and Zenair agreed) that the fixes and new operating limitations are mandatory, but neither has the authority to enforce those for experimental aircraft under the current rules. So, while most owner/operators either fixed their 601/650s per the Zenith repair kits (though a few simply scrapped the airplanes out of an abundance of caution), some chose to ignore the waving red flags, and continued to fly the planes unmodified. Worse yet, some of the pawn these unmodified (and flat-out dangerous, in my opinion) airplanes off on others – buyers who sometimes don't have the knowledge and experience to look beyond the shiny paint and pristine interiors to learn the background on these planes before buying one, flying it, and possibly killing themselves when it comes apart in the air.

You also asked "If i purchase one without the mods that has a few hundred hours on it..why would it all of a sudden not be safe?" It would NOT "all of a sudden" be unsafe. It is already unsafe NOW, according to both the FAA and to Zenair (the designer / kit manufacturer / S-LSA builder). You would literally be flying a ticking time bomb... A gust of wind, too much aileron, or who knows what could be the trigger to initiate flutter, causing the wings to fail and the plane to come apart in the air. (Does that sound alarmist? It isn't - it's basically taken from one of several NTSB reports on these events...)

Zenair developed a comprehensive fix, which includes a fairly major alteration to the wing structure, adding weights to balance the ailerons, and a few other items I cannot recall at the moment. I believe new operating limitations also emerged from that process. Once the Zenair modifications are applied, the airplane appears to be an excellent one. There has not been a single in-flight breakup on one that was modified per the kit. So, while I personally would absolutely not fly in an unmodified CH-601 or CH-650, I would not hesitate to fly in one that has had the mods properly applied. I'd want to see logbook entries referencing the Zenair kit, instructions, etc. as confirmation, then I'd want to visually inspect the plane to see (as best I could) the mods in place. But if all that is OK, yeah, I'd fly it! By all accounts, they are safe, nice flying airplanes.

The "catch" is that while this modification became mandatory for S-LSA versions, it remained "optional" for E-LSA and EAB versions, based on the FARs... (Although the FAA did point out in that SAIB that Part 91.7 requires the PIC to determine if the airplane is in a condition for safe flight – implying that without the "fix" that would not be the case.) So if the owner of the plane you're considering can't show evidence that the airplane has been "fixed" and tries to tell you that it's perfectly safe without the modifications, don't just walk away, but run!

If you like the 601/650 design, you might also want to consider the RANS S-19 Ventarra. It is also a low wing side-by-side design with excellent flying characteristics. People often confuse the two airplanes, although there are some differences if you look closely. There are fewer S-19s out there, but there's a nice one listed on the rans.com website, in the "Pre-Owned RANS" section.

[phatairflyer]

Hello Jim, thank you so much for your time and insight into my question. I did some research prior to your post and decided an un-modified Zenith is scratched off my list..there are a couple out there with the mods done, and one without the mods but the mod kit is purchased and goes with the plane. I do have some skills and the time to probably do the mods and it would give me a chance to look more closely at the build as a whole. But i can pay a few grand more for one with a mod done and that seems the path of least resistance. I don't know what kind of funds i will have for sure yet to purchase a Light sport. It will depend on the selling price of my Tomahawk. I also like the CH750 high wing models and if i had a little more to spend, i would consider an Arion or a Rans as well. I will see where my path leads me, but i am definately NOT going to go with an un-modified 601/650 It's just not worth the risk or anxiety every time i fly it. I hope you have a great day, and i really appreciate your input. ..Kev

[phatairflyer]

Sling 2 , I purchased it with the intent of getting my PPL and i think the Tomahawks are excellent flyers..but i have since learned i may not be able to pass a 3rd class..so instead of risking failure..i decided to go the Sport Pilot route..better safe than sorry.

[Sling 2 Pilot]

Sling 2 , I purchased it with the intent of getting my PPL and i think the Tomahawks are excellent flyers..but i have since learned i may not be able to pass a 3rd class..so instead of risking failure..i decided to go the Sport Pilot route..better safe than sorry.

Good choice.

[JimParker256]

Sling 2 , I purchased it with the intent of getting my PPL and i think the Tomahawks are excellent flyers..but i have since learned i may not be able to pass a 3rd class..so instead of risking failure..i decided to go the Sport Pilot route..better safe than sorry.

Smart decision! I know a couple of guys who tried and failed, and now they are screwed – can't fly Light Sport. And in both cases it's just a stupid technicality that could almost certainly be resolved with a Special Issuance (after a couple of years, and three of four thousand dollars worth of tests, reports, etc.). Just not worth it. Flying Light Sport is a TON of fun!

[phatairflyer]

Yes for me its a possible technicality, Not sure..but i am not willing to take a chance..I am very healthy and would not risk my or anyone else's life if i thought i would be a danger to anyone as a PIC. Its the endless red tape and doctor costs to prove what i already know that i cannot afford. Thank you for your feedback and support. I am anxious to move forward in the next couple months as the day approaches for purchase of a Light Sport. Maybe something really nice..or maybe something classic and fun like the venerable Ercoupe. We will see what life brings me and my wife. Take care , happy flying sir.

[drseti]

the designer did not meet the ASTM design standards when it came to wing loading.

That's because the 601 design dates back to 1984, while the ASTM consensus standards didn't come out until 2004!

[JimParker256]

the designer did not meet the ASTM design standards when it came to wing loading.

That's because the 601 design dates back to 1984, while the ASTM consensus standards didn't come out until 2004!

True, but when the 650 was developed with the intent of making it available as both an S-LSA and as an E-LSA, the design standards were not met (per the FAA's statement). And it just happens that the two designs are extremely similar - especially in the affected areas. And the FAA's SAIB applies to both types...

Aside from that, the ASTM standards are pretty much the same as most designers have followed for years... Including the folks at Zenair, which makes the finding that much more amazing to me. Chris Heintz is not a "shortcut" kind of guy, and his numerous other designs have had zero issues.

[Warmi]

the designer did not meet the ASTM design standards when it came to wing loading.

That's because the 601 design dates back to 1984, while the ASTM consensus standards didn't come out until 2004!

True, but when the 650 was developed with the intent of making it available as both an S-LSA and as an E-LSA, the design standards were not met (per the FAA's statement). And it just happens that the two designs are extremely similar - especially in the affected areas. And the FAA's SAIB applies to both types...

Aside from that, the ASTM standards are pretty much the same as most designers have followed for years... Including the folks at Zenair, which makes the finding that much more amazing to me. Chris Heintz is not a "shortcut" kind of guy, and his numerous other designs have had zero issues.

From what I read they kept denying there was a problem to begin with and frankly that’s their position to this day - as far as I know.

[ShawnM]

Here's a link to the special report put out by the FAA in 2010 about the Zodiac 601 for those interested. It's a real eye opener.

https://www.faa.gov/aircraft/gen_av/lig ... Zodiac.pdf