NTSB asks FAA to ground Zodiac CH-601XL

[rpadula]

im afraid that this is going to create a stigma around the type. Unfortunate, but many pilots will know nothing about the Zodiac CH601XL except that the the ailerons flutter and then you die. I hope your group can do something to help eliminate that Jay.

Hopefully not, although flutter is not something to screw around with.

Few people are concerned now that Rockwell lost a Commander 112 to tail flutter during the test program, so the rep can be overcome. Now, it's just pegged as s..l..o...w.

 

[wabower]

Laugh if you will, but the guy who hangars across from me has a masters degree in engineering, and he once reported some engine roughness in his Bo. I warned him about going back to school.

Maybe this is the time to get things a bit more out in the open. Does the aircraft require a Doctor to be aboard in order to crash? Does the Doctor have to be a medical doctor or dentist? What about optometrists? Ok, the really important one, what about Doctors of Philosophy?

Now one might think the posed questions are pointless and innane and perhaps they are. However, my hangar mate intends to buy a Bonanza and I'd like to get these things clarified. It's a pretty simple question: should I ever take a ride in a Bonanza (or Aerostar or Cirrus). I'd hate for my degree to activate some sort of sensor which then trips the crash=permissible switch.

 

[Clark1961]

Laugh if you will, but the guy who hangars across from me has a masters degree in engineering, and he once reported some engine roughness in his Bo. I warned him about going back to school.

Ahhh, good thing I went the master of science route. Those ME's are low brow types who are only good for designing parking lots and the like (whatever their discipline might be).

Not to get off track from the Zodiac problem. Surely Jay can find an DPE acceptable LSA to rent. Not the cheapest solution but at least it would get'er done. Get the ticket while the knowledge is fresh.

 

[jmaynard]

Not to get off track from the Zodiac problem. Surely Jay can find an DPE acceptable LSA to rent. Not the cheapest solution but at least it would get'er done. Get the ticket while the knowledge is fresh.

There are two problems with this approach:

1) I'll need 5 hours minimum to get signed off to rent solo. (Insurance requirements.) Not prohibitive in itself, except...
2) I live 120 miles away from the closest place that rents LSAs. That means hotel stays and travel expenses.

My schedule is also going to be insane for the next couple of months. I can take a day to get a checkride in, but several days to transition, get my skill in the new aircraft up to CFI levels, then schedule a checkride - and hope weather cooperates - all while staying away from home? That's much more demanding.

 

[Henning]

Before you switch airplanes and/or FBOs, I'd suggest talking to your instructor and your FBO to see what their approach to the issue will be. If they're just sticking their head in the sand and not taking any action at all, it's time to go elsewhere. OTOH, if they're actively keeping an eye on aileron cable tension and staying on top of the rest of the maintenance any aircraft needs, I'd stick with it.

I'm persuaded that proper aileron cable tension will keep flutter at bay. The reason it's not considered an acceptable means of protection by itself is that cables stretch over time, and so it requires active maintenance. While a permanent fix is being researched, as long as the cables are kept taut, and as long as you stay within the aircraft's performance envelope, I believe it'll be fine. If I didn't, I wouldn't keep flying mine.

At this point I'd check all control surface balances just to eliminate any issues there first, and then make sure the cables stay tight and there is no slop. It appears that the horizontal tail control surface, arm and counterweight are improperly designed. Might be any or a combination of several factors. Sounds like it might be aerodynamically over balanced.

The greater concern is why is there any change to the aileron cable tension? What is changing? A properly formed cable will not stretch. None of the pulleys should be shifting, where is the tension going? That is the question I would be seeking the answer to.

 

[Henning]

I'm persuaded that proper aileron cable tension will keep flutter at bay. The reason it's not considered an acceptable means of protection by itself is that cables stretch over time, and so it requires active maintenance. While a permanent fix is being researched, as long as the cables are kept taut, and as long as you stay within the aircraft's performance envelope, I believe it'll be fine. If I didn't, I wouldn't keep flying mine.

The hell they do. I've been cable rigging planes and sail boats for over 20 years. Proper cables will not stretch at any appreciable rate. This is a not very good issue.

 

[tonycondon]

sorry to hear about your checkride jay. any chance you can find a different DE, perhaps in another state, to do the ride?

 

[Trapper John]

The irresponsible acts of the NTSB here are causing hardship to pilots in the United States without real evidence, and that's disgusting....

What is your basis for claiming irresposibility and lack of evidence? Did you actually read the NTSB letter to FAA?


Trapper John

 

[GigG601XL]

What is your basis for claiming irresposibility and lack of evidence? Did you actually read the NTSB letter to FAA?


Trapper John

I don't know about where he is getting it but I read the report and the NTSBreport about the Yuba City accident that the NTSB just released had no mention of flutter other than a phrase that basicly said that there was no physical evidence of it.

I like Jay but he along with the rest of the ZBAG members are the ones that pretty much talked the NTSB into doing this report. The original stated mission of the ZBAG group was to kick in and pay for some 3rd party testing to either support or dispel that there was a problem. It was later that they decided to hand over info to the NTSB at the same time they gave it to Zenith.

So now if the planes are grounded if the planes are grounded it won't be as easy as Zenith finding a fix and telling owners how to fix it the fix will have to be vetted through the FAA.

 

[Geico266]

The Lancair 320/360 has a reputation for tail flutter. Similar "tail flutters and then you die" sort of deal. I think it will stil be alright, though, since people with brains will work to disspell the myths.

Would you buy one now? Resale?

I lost a good friend in AU due to the Zodiac XL. This problem has been well know to the LSA world for years, all I can say is the FAA is about 2 years too late. The entire fleet of Zodiacs should be grounded until the problem is identified an d fixed.

 

[Ted]

Would you buy one now? Resale?

I would definitely buy one. The resale value on them is extremely low, especially for how much plane you get. I suspect there are a number of reasons for that, and the flutter concerns are only one. It's also a very hot plane that has a reputation for requiring a competent pilot to safely fly. This reputation is deserved. Also, it's not very practical, as it's got a small cabin with not much room for luggage.

 

[Henning]

Would you buy one now? Resale?

I lost a good friend in AU due to the Zodiac XL. This problem has been well know to the LSA world for years, all I can say is the FAA is about 2 years too late. The entire fleet of Zodiacs should be grounded until the problem is identified an d fixed.

A Lancair 360? You bet, most of them have the tail mod done now, if not, I'd buy accordingly and do it. As for the Zodiac, it would be foolish to fly unless you knew what the root problem was and mitigated it.

 

[AdamZ]

Jay, I have not read the entire thread but here is the link I got from AOPA. If its a repeat I appologize. I really hope this works out for you!

http://www.aopa.org/aircraft/articles/2009/090415Zenair.html

 

[gismo]

The hell they do. I've been cable rigging planes and sail boats for over 20 years. Proper cables will not stretch at any appreciable rate. This is a not very good issue.

One half to one percent stretch is typical for SS wire rope. IIRC the length varies almost that much with big temperature changes.

 

[Trapper John]

I don't know about where he is getting it but I read the report and the NTSBreport about the Yuba City accident that the NTSB just released had no mention of flutter other than a phrase that basicly said that there was no physical evidence of it.

But even if you toss that one out, it seems like there are plenty of other accidents that seem to be flutter related. I'd be pretty concerned if I were an owner, especially since these failures are happening below Vne and even Vno.

So now if the planes are grounded if the planes are grounded it won't be as easy as Zenith finding a fix and telling owners how to fix it the fix will have to be vetted through the FAA.

If FAA doesn't take any action on the NTSB letter, would that really be the case?


Trapper John

 

[Henning]

One half to one percent stretch is typical for SS wire rope. IIRC the length varies almost that much with big temperature changes.

That is a nearly imperceptible amount that will be less than the tolerance as measured with a tensionometer in this application, and it will happen once on first stretch which should have been accomplished before installation. Typically you can rig a plane every 10 years/2000hrs and what will have changed is the circumferences of the phenolic pulleys have been reduced by wear.

At any rate, that stretch should nowhere near go from proper preload to a slack condition;.

 

[tonycondon]

That is a nearly imperceptible amount that will be less than the tolerance as measured with a tensionometer in this application, and it will happen once on first stretch which should have been accomplished before installation. Typically you can rig a plane every 10 years/2000hrs and what will have changed is the circumferences of the phenolic pulleys have been reduced by wear.

At any rate, that stretch should nowhere near go from proper preload to a slack condition;.

with a wingspan of 27 feet, i would expect 10ish ft long aileron cables could be expected. .5-1% stretch is between .6 and 1.2 inches. How can that not affect tension?

 

[jmaynard]

with a wingspan of 27 feet, i would expect 10ish ft long aileron cables could be expected. .5-1% stretch is between .6 and 1.2 inches. How can that not affect tension?

On top of that, there's a balance cable running directly from one aileron to the other; it's somewhere over 24 feet long.

 

[tonycondon]

On top of that, there's a balance cable running directly from one aileron to the other; it's somewhere over 24 feet long.

cool! thats 1.44-2.88 inches of slack.

 

[Trapper John]

with a wingspan of 27 feet, i would expect 10ish ft long aileron cables could be expected. .5-1% stretch is between .6 and 1.2 inches. How can that not affect tension?

I think the 1/2% to 1% stretch being referred to is the constructional stretch which happens when a wire rope is first loaded. That is pretty much a one-time thing from the strands wrapping tighter against the core provided you put enough load to "take out the slack" so to speak. Then there's elastic stretch, which shouldn't even be measurable at the operating loads in an aircraft control system.


Trapper John

 

[tonycondon]

I think the 1/2% to 1% stretch being referred to is the constructional stretch which happens when a wire rope is first loaded. That is pretty much a one-time thing from the strands wrapping tighter against the core provided you put enough load to "take out the slack" so to speak. Then there's elastic stretch, which shouldn't even be measurable at the operating loads in an aircraft control system.


Trapper John

well alrighty then.

 

[Henning]

with a wingspan of 27 feet, i would expect 10ish ft long aileron cables could be expected. .5-1% stretch is between .6 and 1.2 inches. How can that not affect tension?

Because it's already been pulled out by preload. The wires all work under positive tension that will keep any slack out of they system. If not, it is improperly engineered because at no point is slack allowable in those cables. This goes back to my questions as to just what the ASTM standards actually are and if they're being enforced.

Did you have to go inspect the 421 aileron or tail cables every preflight? You think they went slack? Why would this appear acceptable in an LSA?

 

[Henning]

cool! thats 1.44-2.88 inches of slack.

Aren't you an engineer? Are you being facetious are do you really not understand the material? It's not an elastic stretch, it's a constructive set that happens once. When you build a cable that is length critical, you build it a bit shot for the load stretch. In critical applications, you pull the cable on a test rig which both sets the stretch and tests any swages. Once you install the cable and tension it up, there will be no appreciable change until just prior to failure.

 

[tonycondon]

Aren't you an engineer? Are you being facetious are do you really not understand the material? It's not an elastic stretch, it's a constructive set that happens once. When you build a cable that is length critical, you build it a bit shot for the load stretch. In critical applications, you pull the cable on a test rig which both sets the stretch and tests any swages. Once you install the cable and tension it up, there will be no appreciable change until just prior to failure.

yea yea yea, just giving you a hard time. plus, you of all people should know that engineers don't know jack. you gotta talk to a mechanic to figure out how things really work.

 

[Henning]

yea yea yea, just giving you a hard time. plus, you of all people should know that engineers don't know jack. you gotta talk to a mechanic to figure out how things really work.

Offshore we make project engineers cry....

 

[bullwinkle]

What is your basis for claiming irresposibility and lack of evidence? Did you actually read the NTSB letter to FAA?

Yeah, I'm a Zodiac pilot (even if just a renter) and i would not go so far as calling the NTSB irresponsible! I think they are trying to do the right thing here, and are being appropriately cautious.

After all, if NTSB knew of this problem and said nothing, they'd be ripe for a fat lawsuit the next time a Zodiac goes down, for ANY reason.

.

 

[Henning]

Yeah, I'm a Zodiac pilot (even if just a renter) and i would not go so far as calling the NTSB irresponsible! I think they are trying to do the right thing here, and are being appropriately cautious.

After all, if NTSB knew of this problem and said nothing, they'd be ripe for a fat lawsuit the next time a Zodiac goes down, for ANY reason.

.

Can't sue NTSB, I don't even think for gross negligence. However, this does set up Zenair and ASTM along with all the professionals who developed the standards open for Gross Negligence. I know a lawyer who could sell that to a jury if the industry doesn't act on this before the next one sheds its wings.What is the real problem with this plane? I don't think 6 172s have shed their wings in its entire production run.

 

[Everskyward]

I don't see why these cables would stretch more than cables in any other airplane.

 

[bullwinkle]

But even if you toss that one out, it seems like there are plenty of other accidents that seem to be flutter related. I'd be pretty concerned if I were an owner, especially since these failures are happening below Vne and even Vno.

I believe you are looking at 5 accidents if you throw that one out. Out of 1000 airplanes (according to AMD). That's 0.05%...not exactly a pandemic.

Not saying it's not a concern, but just trying to be precise.

.

 

[gismo]

I think the 1/2% to 1% stretch being referred to is the constructional stretch which happens when a wire rope is first loaded. That is pretty much a one-time thing from the strands wrapping tighter against the core provided you put enough load to "take out the slack" so to speak. Then there's elastic stretch, which shouldn't even be measurable at the operating loads in an aircraft control system.


Trapper John

I agree. As long as the load is reasonably consistent, initial stretch will limit after a short time. It's the temp variations that have a measurable effect in the short term and in that case it's the difference between the Tc of the cable and the Tc of the material supporting the pulleys (i.e. aluminum or plastic). Since Al has a higher Tc, the cable tension will decrease in the cold and increase in warmer conditions. On my airplane there is a chart or graph that shows the proper tension for any specific temperature and I assume that the intent is to make them tight enough for flight in cold air without making them so tight they strain or break something when it's warm.

 

[bullwinkle]

Can't sue NTSB, I don't even think for gross negligence. However, this does set up Zenair and ASTM along with all the professionals who developed the standards open for Gross Negligence. I know a lawyer who could sell that to a jury if the industry doesn't act on this before the next one sheds its wings.What is the real problem with this plane? I don't think 6 172s have shed their wings in its entire production run.

But how many 172s had any flutter issues? If it is flutter, and is a result of the cable tension, that seems like the problem. If the ailerons need better balancing, that can be addressed. If there is a deeper structural problem, then all bets are off as to when or even if the problem will be solved.

I think it's interesting that the original hingeless design has had no issues at all, and all this started when they changed to a conventional hinge to make people feel better about it. A apparent classic case of people shooting themselves in the foot by reasoning based on emotion rather than actual data.

.

 

[SkyHog]

I believe you are looking at 5 accidents if you throw that one out. Out of 1000 airplanes (according to AMD). That's 0.05%...not exactly a pandemic.

Not saying it's not a concern, but just trying to be precise.

.

Thank you. Sometimes Trapper John gets so blinded defending the government in every decision they make that he misses the fine details like "take one away from 6 and you have 5." Neither 5 nor 6 are very large numbers...

 

[Trapper John]

I believe you are looking at 5 accidents if you throw that one out. Out of 1000 airplanes (according to AMD). That's 0.05%...not exactly a pandemic.

Not saying it's not a concern, but just trying to be precise.

Not to pick nits, but that's 0.5%, or in other words 1 out of 200...

If 1 out of 200 C-172's wings folded up, there would be and AD issued pronto. And I'm pretty sure 0.5% of the V-tail Bonanza fleet didn't shed their tails before ADs were issued...


Trapper John

 

[Trapper John]

Thank you. Sometimes Trapper John gets so blinded defending the government in every decision they make that he misses the fine details like "take one away from 6 and you have 5." Neither 5 nor 6 are very large numbers...

But not too blind to check calculations! See above.

You're welcome,
Trapper John

 

[Trapper John]

I agree. As long as the load is reasonably consistent, initial stretch will limit after a short time. It's the temp variations that have a measurable effect in the short term and in that case it's the difference between the Tc of the cable and the Tc of the material supporting the pulleys (i.e. aluminum or plastic). Since Al has a higher Tc, the cable tension will decrease in the cold and increase in warmer conditions. On my airplane there is a chart or graph that shows the proper tension for any specific temperature and I assume that the intent is to make them tight enough for flight in cold air without making them so tight they strain or break something when it's warm.

That's a very good point and I wonder if the designer relying on cable tension to prevent flutter considered thermal effects in his/her decision.


Trapper John

 

[Henning]

I don't see why these cables would stretch more than cables in any other airplane.

Yeah, huh? It doesn't happen without some failure of something. What is the failure is the question. Some are easy to mitigate by technique, some require re-engineering things. I would not fly one again unless I was satisfied I knew that answer.


What are the LSA standards for setting Vne? What is Vne on the 601XL? How fast will it go in a powered up descent? Could it simply be DA pilots flaunting LSA limitation making the plane go faster, "120 my a--, watch this, I can peg to 160...."?

 

[jmaynard]

What is Vne on the 601XL?

For the SLSA version and some kits, it's 140 KIAS. (Earlier kits has a somewhat higher Vne; I don't know why it was changed.) Vno is 108 KIAS.

How fast will it go in a powered up descent?

I haven't had mine above 120 KIAS. That was in a power-on descent in absolutely smooth air.

Could it simply be DA pilots flaunting LSA limitation making the plane go faster, "120 my a--, watch this, I can peg to 160...."?

That doesn't seem to be the case, from the folks I've spoken to.

 

[rpadula]

Not to pick nits, but that's 0.5%, or in other words 1 out of 200...

If 1 out of 200 C-172's wings folded up, there would be and AD issued pronto. And I'm pretty sure 0.5% of the V-tail Bonanza fleet didn't shed their tails before ADs were issued...


Trapper John

Heck, Cessna grounded the entire fleet of Conquest II's (441) when a tail fell off of one and killed seven people. Flutter-related. They redesigned the horizontal stabilizer and replaced it on about 100 planes.

 

[mcjon77]

I believe you are looking at 5 accidents if you throw that one out. Out of 1000 airplanes (according to AMD). That's 0.05%...not exactly a pandemic.

Not saying it's not a concern, but just trying to be precise.

.

That "1000 airplanes" number seems fairly high. I suspect that they are counting ALL 601 variations, including the 601 HD and the 601 HDS, neither of which has had these problems. There are only about 300 flying 601XLs registered in the U.S. Of those, perhaps 60-70 are factory made SLSAs from either AMD or Czech Aeroworks(this is from the FAA database).

I know that they are somewhat popular in europe and other countries, but 1000 601XLs actively flying seems a bit too high, but I could be wrong.

 

[Henning]

I believe you are looking at 5 accidents if you throw that one out. Out of 1000 airplanes (according to AMD). That's 0.05%...not exactly a pandemic.

Not saying it's not a concern, but just trying to be precise.

.

That rate is not tolerated in certified aircraft by any means. Is it a trade off we are willing to make to the economies of LSA? Not my call, but let me know if it is acceptable so I can make my own decisions accordingly. As it is, just by looking at the LSAs at S-n-F and OSH, fully half of them I wouldn't fly because I spotted glaring design and construction errors that fall outside my personal standards, and that was without opening them up.