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Throttle Cable Severs in Flight

Roadjunkie1 said:
OK: it looks like the bracket was modified to drop the cable attachment about an inch lower. That would not make that much change in the length of the cable needed.

BUT: here's what I don't understand. Will someone please explain (say, the OP....): in the OP post #1, it shows the modified bracket with the cable housing attached and the broken cable protruding from that. The steel rod that attaches to the throttle body is also blurry but visible. Post #13 shows a brass rod that the cable was once attached to that has now broken off. That brass rod or tube has a threaded end with a nut on the end not hooked to the cable. Post #24 shows the steel push rod attached to the throttle body arm. Where does the brass fitting that was attached to the cable come in? What was it pushing on? What was it sliding through, if anything? Was that in the cable housing? There should be a sleeve that might have departed company with the cable when it broke. Was it ever there or was the brass rod coming out of the cable housing before the cable broke? But then what is the purpose of the brass nut on the brass fitting? :confused::confused::confused:
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It's not brass.... It's the same rod in both of the pictures. Post 13 and 24.

That is a normal end on this type of cable.
 
I would be curious to know what ACS thinks. It may not be their cable, but they might be able to shed some light.
 
gasman said:
Chances are it fell off when the cable broke.... https://vansairforce.net/community/showpost.php?p=1718313&postcount=28
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skylor said:
Not likely, because the tube is swaged into the cable jacket end fitting. The cable broke the way it did because the tube was previously removed and it wasn’t properly supported where it joins the threaded rod swage joint.

Skylor
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I have to agree with this. That cable did not get pulled apart. It broke by vibration because it was not supported by the tube. It did not fail due to not enough play between the firewall and the engine bracket. The case may try to pull back the carb bracket. But the cable is only secured at one end... the control end when it is locked. The other end is connected to a rotating shaft that would only place a pull on the cable at idle cut-off. And at that point, the cable would be in a full stretched condition that would not be subject to vibration.

With the cable in full WOT condition, the cable could act as a whip extended that far out without support, and could vibrate up and down and cause a failure...... I agree with those that say the cable was altered by removing the support tube, for some reason?? Only the builder will know that answer.

Think about how many inspections that aircraft went through, without anyone seeing this issue evolve.
 
gasman said:
Think about how many inspections that aircraft went through, without anyone seeing this issue evolve.
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Which in my opinion (which this thread is full of) should raise some level of doubt that it was missing before the cable failure occurred, but at this point, anything is possible.
 
Hmmmmmm

rvbuilder2002 said:
Which in my opinion (which this thread is full of) should raise some level of doubt that it was missing before the cable failure occurred, but at this point, anything is possible.
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Or it was looked at and "appeared" to be OK. If one does not know how something is supposed to look, they will not think it a problem. How many times have I seen things on an airplane and thought....'Huh. That's interesting. Not the way I would have done it but.....'

Common things are common, as we say in the medical field. Most all things will "look" the way they are supposed to. But customizing some things can occasionally cause issues. The fact that the fitting holding the cable and the lack of slack from the fitting to the firewall were not seen as an issue.... Which is not to put blame on anyone and might not have been the cause of this cable failure. It is a physical thing and physical things occasionally do break...sometimes without an obvious reason. It is sometimes difficult to look at something and SEE an issue. We have ALL missed things! Over the years I have looked at things I did several decades ago on SuzieQ and thought....'Huh...why did I do (or not do) that?' That is the advantage in having put her together myself. After reading this thread I had to go out and look at my cable setup to see if it looked right.:eek: It 'looked' pretty good! More importantly it worked the way it was supposed to. I had the advantage of several decades of working on airplanes before I started my build and was able to put things together the way I had seen them work on other airplanes.

In the process of recently adding some new things to SuzieQ I have found things that were OK but I have changed to be better or more along the lines of current thinking. And knowledge from several more decades of working on airplanes!

This issue had a good outcome in that it failed at the right time and the OP had the wherewithal and piloting skills (!) to have been able to land without issue. AND it started this thread which will educate the rest of us to question things that might look....'interesting'..... It is a great advantage to have the "inspection authorization" to work on SuzieQ and be the one to do her condition inspections. I do, occasionally, have someone else look at things as well. Can't have too many eyes....:)
 
Roadjunkie1 said:
Or it was looked at and "appeared" to be OK. If one does not know how something is supposed to look, they will not think it a problem. How many times have I seen things on an airplane and thought....'Huh. That's interesting. Not the way I would have done it but.....'

Common things are common, as we say in the medical field. Most all things will "look" the way they are supposed to. But customizing some things can occasionally cause issues. The fact that the fitting holding the cable and the lack of slack from the fitting to the firewall were not seen as an issue.... Which is not to put blame on anyone and might not have been the cause of this cable failure. It is a physical thing and physical things occasionally do break...sometimes without an obvious reason. It is sometimes difficult to look at something and SEE an issue. We have ALL missed things! Over the years I have looked at things I did several decades ago on SuzieQ and thought....'Huh...why did I do (or not do) that?' That is the advantage in having put her together myself. After reading this thread I had to go out and look at my cable setup to see if it looked right.:eek: It 'looked' pretty good! More importantly it worked the way it was supposed to. I had the advantage of several decades of working on airplanes before I started my build and was able to put things together the way I had seen them work on other airplanes.

In the process of recently adding some new things to SuzieQ I have found things that were OK but I have changed to be better or more along the lines of current thinking. And knowledge from several more decades of working on airplanes!

This issue had a good outcome in that it failed at the right time and the OP had the wherewithal and piloting skills (!) to have been able to land without issue. AND it started this thread which will educate the rest of us to question things that might look....'interesting'..... It is a great advantage to have the "inspection authorization" to work on SuzieQ and be the one to do her condition inspections. I do, occasionally, have someone else look at things as well. Can't have too many eyes....:)
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Agreed! We frequently hear in these forums about planes that have been flying for many years with multiple owners, had multiple pre-buys, multiple condition inspections by different A&P's etc., yet had safety critical deficiencies since day 1! Having something like that overlooked does not seem so unusual to me.

Skylor
 
So a big question to those who have RVs for many years, do you have to replace the throttle cable after a certain amount of operating hours, like you do for the fuel line? And how do you even do the inspection of the throttle cable right at where the cable meets the crimped end of the pushrod that connects to the fuel control?

Or should the cable last for the lifetime of the airplane, or until the outter silicon sheathing wears out because of rubbing or heat exposure?

I don't remember I ever see the cables end of either the throttle or the mixture cable while installing them in my RV8, just the exit pushrods. I just tighten the cable nuts to the respective brackets in the firewall forward kit.
 
PhatRV said:
So a big question to those who have RVs for many years, do you have to replace the throttle cable after a certain amount of operating hours, like you do for the fuel line? And how do you even do the inspection of the throttle cable right at where the cable meets the crimped end of the pushrod that connects to the fuel control?

Or should the cable last for the lifetime of the airplane, or until the outter silicon sheathing wears out because of rubbing or heat exposure?

I don't remember I ever see the cables end of either the throttle or the mixture cable while installing them in my RV8, just the exit pushrods. I just tighten the cable nuts to the respective brackets in the firewall forward kit.
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You can expect the push pulls to have a very short service life if not properly protected from heat. There’s plenty of info on here so worth reading up on.
They’ll usually give plenty of warning but that warning shouldn’t be ignored.
 
Richard Connell said:
You can expect the push pulls to have a very short service life if not properly protected from heat. There’s plenty of info on here so worth reading up on.
They’ll usually give plenty of warning but that warning shouldn’t be ignored.
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I realize the heat will cause the degradation in the push pull cable. But the question is how can a person even do the condition inspection of the cable at the location of the crimp to detect the failure like in the original post, unless you remove it from the bracket?
 
Firewall forward push/pull cables.

PhatRV said:
I realize the heat will cause the degradation in the push pull cable. But the question is how can a person even do the condition inspection of the cable at the location of the crimp to detect the failure like in the original post, unless you remove it from the bracket?
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Good point. The throttle cable in the Cub has been there since 1946 and occasionally needs to be lubricated. It has over 4000 hours on it and shows no signs of failure or being worn out. Of course, that was back when they MADE things!

I have not heard of many of this type of cables failing. Even on the older airplanes I have worked on. Smaller cables like heat, ventilation, etc: yes. I have replaced those, including on the Cub. But larger, stouter cables I have not seen as a problem. It would be interesting to know how many RVs have had to have their (larger) throttle, prop or mixture cables replaced. Problem is, there are so many different types. The Cub and SuzieQ are simple push/pull cables. No vernier mechanisms. Look up cables in ACS and some have a "lifetime lubrication". What does that mean? Whose lifetime...?;)
 
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Broken Throttle Cable

I've had exactly the same failure with an ACS throttle cable. Noticed no throttle response during a practice instrument approach 50 miles from home, and started to head toward my home airport. It didn't take long to realize that a very slight throttle creep would make that impossible, so picked a closer airport, and manged power on approach with mixture (i.e. let it quit/windmill periodically). Landing turned out well. This happened at about 1000 hours.

The cable failure was identical to the one in this thread. Checking the cable installation, I came to the conclusion that it was not at fault - it simply provided the slight flex required to stay aligned with the throttle lever, and little more. I further concluded - although I'm sure others here will chime in why hasn't his happened to more folks with this cable - That it was the fault of the insufficient ruggedness of the ACS design. There is vibrational stress at the cable crimp interface to the end piece, and their cable is not thick/rugged enough to survive the vibration. So, I replaced all my cables with McFarlane cables in their certified line, and boy, you can see the higher quality and greater thickness of the inner cable.
 
Thanks for the update. It seems to be a good idea to upgrade the push-pull cable when an opportunity arises especially in a high time RV.
 
PhatRV said:
Thanks for the update. It seems to be a good idea to upgrade the push-pull cable when an opportunity arises especially in a high time RV.
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Based on two known failures out of what, 10,000 plus cables? Oh, wait, mixture, and prop, 25,000 ? Many on high time RV’s.
Vans has used ACS for a long long time. Thus far, one failure is likely poor installation. The other? Would like to see pics of how it was installed.

I would be looking at the installation making sure appropriate slack is in the cable between the firewall and bracket. I have dissected the ACS cable and refuse to believe it isn’t robust enough for this application when properly installed.

I should have added that ACS supplies these types of cables for other apppications like Dump Truck PTO’s, which are very high vibration. The PTO installation requires a slack loop.
 
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I wonder if ACS changed their production method somehow? Maybe they're using laser-cut cables now... :/
 
Who made the old green cables?
.
 

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mburch said:
Those look like the same green cables I bought from Vans, which were made by Cablecraft:

20080311_label.jpg


(not for use on aircraft!)
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And Cablecraft sees to be a franchise-type operation, with cables made on-site. I needed a cable made to a custom length, found a “distributor” right in Reno, drove up, and the fellow made me one in about twenty minutes. Which tells me that you don't know, for sure, WHO made your cables, or where….they aren’t all spit out on the same assembly line.

Not sure if it makes a difference or not - just throwing my experience out there.
 
Calls into question the cable I dissected years ago. Might not have been ACS ;(.
I do know my current cables, from 2005 ‘ish, are ACS and a replacement cable from around 2015 is also. All supplied by Vans.
 
Throttle/mixture cables: GREEN

mburch said:
Those look like the same green cables I bought from Vans, which were made by Cablecraft:

20080311_label.jpg


(not for use on aircraft!)
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That's what I have in SuzieQ from about 1996. They looked pretty rugged at the time. Still do. And no hint of malfunction. They are in an area that is not in direct line with exiting hot air from the cylinders but still in a hot environment. I saw the "not for use on aircraft" disclaimer and immediately put it in the airplane!:D Hard to say where it actually came from or who made it. As long as it works, I'm fine. Elevator trim cable seems to have been made by the same company.
 
I think Cable Craft (green sheath) and ACS (black sheath) are still supplied depending on the application.

Engine control cables that utilize a quadrant (threaded rod on both ends) have always been Cable Craft cables as far as I am aware.

The manual pitch trim cables have always been from cable craft (two styles... one with a knob, and one with a threaded rod for a clevis connection to a trim lever like on the RV-4

Engine control cables with knobs have always been from ACS.
 
To the OP: How many hours since the last Condition Inspection, and do you check for play in your cables? A few condition inspections ago I noticed some play in my throtal cable. I could never identify the sourse, so I just replaced it. Components rarely fail without some warning, it is just that we often miss or ignore the warning.
 
rvbuilder2002 said:
I think Cable Craft (green sheath) and ACS (black sheath) are still supplied depending on the application.

Engine control cables that utilize a quadrant (threaded rod on both ends) have always been Cable Craft cables as far as I am aware.
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Thanks for that clarification Scott - I should have mentioned that I have a quadrant.
 
Throttle Cable Replaced

JonJay said:
Based on two known failures out of what, 10,000 plus cables? Oh, wait, mixture, and prop, 25,000 ? Many on high time RV’s.
Vans has used ACS for a long long time. Thus far, one failure is likely poor installation. The other? Would like to see pics of how it was installed.

I would be looking at the installation making sure appropriate slack is in the cable between the firewall and bracket. I have dissected the ACS cable and refuse to believe it isn’t robust enough for this application when properly installed.

I should have added that ACS supplies these types of cables for other apppications like Dump Truck PTO’s, which are very high vibration. The PTO installation requires a slack loop.
Click to expand...

I replaced the severed cable yesterday with the CT BLK THROTTLE 50.5 from Vans. The install went really well, but it wasn't what I'd call easy. There was no issue with the length of the cable; it was sufficient to included a small loop of slack. I inspected the mixture cable, and just like the throttle cable, the swedged portion at the end of the threaded section had separated. There was no wear of any kind on the strands within. I crimped the swedge back in place with channel-locks and will replace it properly when I return to my home airport.
 
airshawn58 said:
I replaced the severed cable yesterday with the CT BLK THROTTLE 50.5 from Vans. The install went really well, but it wasn't what I'd call easy. There was no issue with the length of the cable; it was sufficient to included a small loop of slack. I inspected the mixture cable, and just like the throttle cable, the swedged portion at the end of the threaded section had separated. There was no wear of any kind on the strands within. I crimped the swedge back in place with channel-locks and will replace it properly when I return to my home airport.
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Hmmmm....so the only two known instances of this happening, at least in the RV fleet, are both on the same airplane.
 
airshawn58 said:
I replaced the severed cable yesterday with the CT BLK THROTTLE 50.5 from Vans. The install went really well, but it wasn't what I'd call easy. There was no issue with the length of the cable; it was sufficient to included a small loop of slack. I inspected the mixture cable, and just like the throttle cable, the swedged portion at the end of the threaded section had separated. There was no wear of any kind on the strands within. I crimped the swedge back in place with channel-locks and will replace it properly when I return to my home airport.
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That should not be there.... Can you post a picture of the loop?
 
For Safety's Sake

Not all airplanes are RVs, not all RV owners use VAF, not all people who use VAF post, and not all posters have shared everything they have seen.

There are more cable malfunctions in Heaven and Earth than are posted of in Doug's website.

Trying to diminish a poster's experience doesn't serve Safety. Why not just read, inquire if interested and reflect? Go nuts in 'Ongoing Maintenance.'
 
I'm only questioning whether this just might be a problem not with the cables, but with their installation in *this* case. It seems highly improbable, to me, that two cables would fail in the same manner on a single aircraft, but not (apparently) on thousands of others.

This would point me towards either a fault with a particular lot of cables from the manufacturer, or a fault with the installations in this situ, or a fault with how they're operated.

Assuming the lot they came from was large, why hasn't this been noticed by anyone else (that we know of)? Or, if they came from two *different* lots, what does that imply?

I want these cables to work and not fail, too...I just am a bit skeptical that this is not something to do with how they were installed in this case (why did they need to mod the cable bracket? It appears there was essentially no slack between the firewall and the bracket? Etc.).
 
Sorry if I missed this in part of the earlier discussion.

A push - pull cable needs to be guided or sleeved the entire length or when pushed the end will flex/fold.
If the section in red has come loose from the crimp, it will allow the rod end to flex/fold each push. Each flex/fold will stress the cable portion.
The guide shown in red was missing in the pictures provided. We could assume that when the end came loose on the throttle cable that the guide fell off in flight.
I believe airshawn is also telling us that the prop cable guide has also come loose.
For our own concerns and inspections we can always make sure the guide in intact and does not move with cable operation.
 

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I don’t think anybody is questioning the OP’s experience. However, it has been suggested that the ACS cable is not adequate for the job. If so, this would affect most of the Vans fleet, thousands of aircraft.
Everyone is trying to understand why the cable failed and how to inspect for a similar case in their aircraft.
Blaming the cable is a tough swallow….
 
skylor said:
If the original poster's plane had the outer tube removed from the cable end that is shown in your picture, then the swaged part of the cable would see a lot of bending load from engine vibration right where the cable enters the swage fitting. Bending load here would effectively cause the swaged cable end to cut through the cable over time. The missing outer tube ensures that the cable and the swaged end remain in-line with each other so that there is no bending at this point.

I am guessing that the original builder couldn't get enough travel towards the idle position on the throttle and may have removed the support tube instead of making adjustments elsewhere such by reclocking the servo control arm or installing a shorter arm (Avstar does sell different length and shape throttle and mixture arms). If this was the case, bad idea...

Skylor
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I think Skylor is onto it here, given that the same failure seems to have occurred on another cable in the same installation. It would be nice if we had pictures of that second instance.
 
I Flew Back to Home Airport on Monday

...lot's of inputs and theories. Admittedly, you all have me at a huge disadvantage; I'm not a builder, A&P, or even particularly mechanically minded. Can someone tell me how much "slack" "play" etc. the cables should exhibit between the firewall, last brace and fuel control arm?

I'll take some more pictures/vid of all the power related connections/cables. I flew my RV home on Monday after several loops in the pattern at the airport I was held-up at. The throttle cable movement was smooth and consistent; I had every confidence in it.

There is an answer to this odd, mystery event; I haven't ruled anything out -install, defective cable, bad piloting, really bad luck, everyone should be concerned/only I should be concerned, etc. Thanks to everyone for weighing in. sle
 
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JonJay said:
it has been suggested that the ACS cable is not adequate for the job. If so, this would affect most of the Vans fleet, thousands of aircraft. Everyone is trying to understand why the cable failed and how to inspect for a similar case in their aircraft.
Blaming the cable is a tough swallow….
Click to expand...

Nobody is reasonably suggesting ACS cables are inadequate. There is some tendency here in this discussion to presume these cables are without potential failure and that is also not reasonable.

I shared an anecdote of a binding ACS cable installed with all its parts and pieces in nearly a perfectly straight line from a center console to the fuel servo, on centerline between exhaust stacks and heat shielded. That cable bound up and froze in the idle position at 23 hrs of operation.

I can recall thinking after the fact that I might have felt some friction near the idle position before it jammed. Had I been more flexible to the idea that some of these cables may carry a defect I might have been more sensitive to that small symptom. What cable did I replace it with?...ACS of course.

The OP's case may not be a failure of the cable, it may be. Here in the Safety forum it is a datapoint for each of us to consider, rather than one to rebuff.
 
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wawrzynskivp said:
Nobody is reasonably suggesting ACS cables are inadequate. There is some tendency here in this discussion to presume these cables are without potential failure and that is also not reasonable.

I shared an anecdote of a binding ACS cable installed with all its parts and pieces in nearly a perfectly straight line from a center console to the fuel servo, on centerline between exhaust stacks and heat shielded. That cable bound up and froze in the idle position at 23 hrs of operation.

I can recall thinking after the fact that I might have felt some friction near the idle position before it jammed. Had I been more flexible to the idea that some of these cables may carry a defect I might have been more sensitive to that small symptom. What cable did I replace it with?...ACS of course.

The OP's case may not be a failure of the cable, it may be. Here in the Safety forum it is a datapoint for each of us to consider, rather than one to rebuff.
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So, was it replaced with the same exact cable in the exact same location, and how did the new cable hold up?

Was it the cable or the location?
 
gasman said:
So, was it replaced with the same exact cable in the exact same location, and how did the new cable hold up?

Was it the cable or the location?
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Yes same length, same make. Same mounting, everything the same except the binding from the original cable. No problems whatsoever four years hence.

I spent the unreimbursed effort to return the cable to ACS for a manufacturer engineering investigation and that didn't lead to any response shared with me. Still worth doing and worth sharing with the community.
 
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