Paraski incident reprinted from Yahoo list

[Bruce Brown]

Hello All,

I believe there may be important safety lessons to be learned from
the following accident report.

Before I get to the report I would like to note the following
though: All of our machines have critical attachment points and
many
have nicopress fittings. This type of failure could have happened
on
essentially any machine out there.

That said, there may or may not be some legitimate lessons to be
learned that are specific to the ParaSki design.

When I bought a ParaSki, my primary goal was to surround myself
with
the safest machine available. When my student and I emerged from
this crash with ZERO injuries, I thanked:

* The deity and my very good luck
* ParaSki for designing a frame that protected both occupants
Completely
* My modest skills as the PIC

In spite of the failure, I believe the descent and impact would
have
been at least as bad and probably worse in most other models.

Please resist the urge to turn the discussion that may follow in
to
a brand bashing festival. Beyond that, please take what lessons
you
can from the following report, video and Pictures and most of all -

fly safe!!!

This is the report I filed with EAA -

Flight Safety Report - Accident/Mechanical Malfunction

Per the requirements of FAA Exemption #9784M and the EAA UFI
program, please accept the following Flight Safety Report on an
Accident/Mechanical Malfunction.

Date of Mishap: 5/27/2007
Type: Accident / Mechanical Malfunction
Ultralight Owner: Barry Foer
Address: XXXXX
Phone: xxx/xxx-xxxx
EUL #: XXX
Registration #: EXXXXX

Pilot Information: EUL #XXX Barry Foer
Two Place Training Aircraft Information –
Manufacturer: Propulsion Parachute/ParaSki/Delta Motorise, Inc.
Model: Fox 503
Aircraft Serial Number: F-503-C 3/0-500-00-02
Engine Serial Number: 4795614 Rotax 503
Type: Land PPW
Empty Weight (lbs.) 270
Maximum Fuel (gallons): 10
Power off Stall Speed (kts.): N/A
Full Power Flight Speed: N/A

Accident Information -
Injuries: None
Fatalities: None
Location: Warrenton Air Park 7VG0

Description and probable cause:
The aircraft was inspected and flown on 5/26/2007 with no visual
or
performance based indication of any mechanical problem evident. On
the morning of 5/27/2007 after a complete preflight inspection of
the aircraft had been performed, I taxied to the runway for set up
and departure at approximately 8:15 a.m.

Winds were at zero, temperature was approximately 80 degrees F and
weather was not otherwise a factor.

The kite up, rolling inspection and lift off were all routine.
Having established normal climb, a right turn was executed at
approximately 125 feet AGL to avoid crossing runway 4/22 and
establish a heading allowing for additional climb out near the
runway areas.

At approximately 150 AGL the Nicopress Oval Sleeve used to eye-
splice the right side aircraft cable riser failed. The failed
cable
had served to attach the machine to the "A" lines of the ram air
wing. The failure of this cable immediately deformed the right
half
of the wing resulting in a complete collapse of the entire right
half of the wing.

The aircraft immediately:
* Lost sufficient lift to sustain altitude
* Veered to a nose down attitude
* Rapidly descended in a substantial rightward spiral to impact
with
ground

The airframe is a complete loss. There were no injuries to the
student or instructor.

Additional Pilot Observations:

With the loss of the right half of the wing, pilot control was
effectively limited to:
* Modest steering response from the left side of wing allowing the
spiral to be slowed but not stopped
* Throttle appeared to allow a slight reduction in the rate of
descent but was totally insufficient to significantly prolong or
sustain flight
* Modest flare response from the left half of the wing was evident
immediately prior to impact

The airframe performed an exceptional job of protecting both
occupants and distributing the impact energy throughout the
airframe.

The time from failure to impact was not greater than 5 to 6
seconds.

The flight path was over open field with plenty of runway ahead
and
an emergency "plan and spot" in sight. There was an ample amount
of
open space surrounding the runways to provide for safe operation
plus an extra "comfort" margin. The loss of both lift and control
authority at the same time did not permit the execution of any of
my
pre-planned emergency options. The rightward spiral forced me down
in an area compromised by both trees and hangers further
complicating the landing. I am uncertain that any additional
planning could have provided a better alternative for this type of
failure.

Video - http://video.google.com/videoplay?docid=-3594925962897630451


Pictures –
http://s65.photobucket.com/albums/h201/barryfoer/ChuteFailure/

Barry Foer
Alexandria, VA
http://bfoer.homestead.com/home2.html

[kilowatt]

Thank you for posting the information. I am grateful that the pilot and student were not injured.

Nicopress fittings have been used in the aviation industry for years and we use them, although not as extensively as years past; in the utility industry. We deal with this same type failure in the utility industry very frequently.

One point of consideration involves not only Nicopress type fittings, but any compression fitting, is that one must expect a certain and prevailent amount of fatigue to occur to the material being spliced when the material is in a state of constant flex. The splices are as strong as the cable but will be subject to premature failure when the cable is in a state of constant flexing, especially when the flexing is located near the end of the fitting itself. This is especially prevailent when the compression fitting is held stationary while the cable is allowed to flex.

We have observed that when in a state of flex, the cable will most often fail right at the end of the compression or just inside the fitting at the cable entrance to the fitting. The compression of the fitting holds the material so tightly that it disallows the individual strands of the cable to move with the flexing motion.

Grasp the end of a straw very tightly in your hand with a portion extending out, then start flexing the straw with your other hand by placing side load directly to the end. Most likely it will fail at the point where it enters your fist.

A big issue we battle is diagnosing cable failures withing our compression fittings as the degradation of cables is very, very difficult to visually observe and failure can be almost impossible to predict. We use an ohm meter and compare readings across the splice against readings of a good section os the cable, next to the compression. If readings are out of tolerance, the compression fitting is replaced.

Regards,

Kilowatt

[BCAUTOSOUND]

I don't think I could ever make myselft comfortable flying with cable risers. The connectors just look like a place of possible failure. I don't really understand why PPC manufacturers still use those cables as compared to riser straps. I know theaoretically the cables are stronger. however, the risers have a human touch at the seams their weakest point. Cables have a crimping tool a mechanical touch at the point of highest failure.

[RandyV]

Bruce,

I assume Paraski will be involved in the investigation to determine the cause of failure and propose a solution. Really quite positive that everyone walked away but a bit scary in the fact that there was no way to detect that a failure was going to occur.

Randy

[Rich K]

We all gain from the experience of others and thankfully the report was available and the flyers are here to tell the story.

The responses to the report has been educational and interesting.

I too have cables with nicopress fittings on my Summit.
On my craft there are two to each end of the cable.

Does having that redundancy have any advantage or would a timely replacement of the cables be more advantages?


Sure pleased nothing more then a PPC was damaged and some great flying indeed!


Rich K

[barryfoer]

Hi Bruce,

Thanks, I was just getting ready to add this report here for posterity.

I also posted to the General Discussion forum in hopes that some additional discussion might reveal better preflight or inspection proceedures.

Thanks to all of you for the positive comments :-)

Best to you,
Barry

[mignazito]

Because the Paraski designed wings use separate risers to A,B,C and in this case DE (4 risers, some have 5) that are not tied together, a cable failure is more of an issue than it might be in other cases. Most PPCs have 2 cables on each side and if tied together at the top have some redundancy. Had another cable other than the A line failed, I suspect the outcome would have been less severe.

Kilowatt and others who know Nicopress fittings: The sleeve does not "look right" to me. I have made a couple dozen of these and they seem to my mind to look different than what I see in the pictures. I need to go to my hanger and look tomorrow. It appears the cable pulled out of the oval sleeve, but that sleeve looks more like a stop sleeve than a correct oval to me. Maybe it failed to a new shape? It also has "bumps" instead of dimples on the outer edge which looks odd to me.

Don't be lulled into complacency with strap risers. They too could fail for a variety of reasons and often have little or no redundancy. The inner fibers are also concealed by the jacket where an immenent failure could be lurking unseen. Any mechanical device made by humans is subject to failure from human error, wear or fatigue.

New cables and straps should be "proof tested" prior to use, but I know of no one in ULs who does this including myself. I make my own cables too. I might start doing it now gievn this incident.

Marty

[RandyV]

It sure troubles me that there was no indication of a problem with the fitting. I am not familiar with Nicopress fittings other than I have them on my machine but this is one of eight cables so the fitting failed under a load of less than 100 pounds. For a 1/8-inch cable connection to not feel loose and fail carrying less than 100 pounds is just downright scary.

Randy

[woodyking]

I worked with wire rope for many years (27) as an Ironworker, the old standard eye was done as a "liverpool" splice, I could probably still do one in my sleep, but about 15-20 years ago, the industry completely went to the molly hogan with a swage over the tails. This eye will always break somewhere other than the swage when pulled to destruction when the cable is NEW. What is normally done on PPCs would never be done on contruction, which is just looping the cable around and putting a swage on it. Using two swages does a great job of indicating movement between the cable and swage, and should be used on any critical cable. Of course, failure from fatigue at where a cable enters the swage is going to be the main killer of a cable in motion, as ours are. Even when they pivot on smooth points like shackles, the slight resistance causes more fatigue where the cable enters the swage.
I've made a few sets for Paraplanes, and have followed the two swages separated by a couple of inches to make inspection easy as far as if any slippage occurs. Having this short section of double cable does also help reduce the bending at swage entry. Woody

[mignazito]

Double swagging would certainly prevent a slip like that experienced in this incident. Some use it, some do not. From what I have read, for copper or stainless compression swages, little or no added strength is provided by double swagging. Given this incident of slippage, double swages might be a consideration. Supposedly copper swages provide about 80% of rope strength for the ASSEMBLY. Interestingly stainless steel swages on stainless steel rope are supposed to provide 100% of rope strength. You seldom see stainless swages however since they are very expensive and require special tools to compress.

Overdesign is the way this situation is handled in general. The "proof" strength of the ropes AND thier end connections should be well below any loads ever impossed. The proof load is that maximum load to which the assembly can be subjected with no damage or permenant deformation. Per ASTM the proof stress should be at least 4.5 times the gross weight. This allows for a 2G manuever with a 1.5 gust and 1.5 safety factor. At say a 900 lb gross weight for 8 equally stressed ropes this would be a minimum proof load of 506-1/4 lbs per rope. The A & B ropes are probably more highly loaded. Even if the ropes are 1/8" as I recall the breaking strength of 1/8" rope is about 1400 lbs with swages (1750 without) or 37% of breaking strength for a properly made 1/8" nicopress swage at 506 lbs. I think the Paraski risers are 5/32", but I need to check that when I go to the hanger today.

Inspection of the ropes before flight to see if there is any slippage might be in order. I do not know if movement might be seen before the rope "let's go", but I look at them just the same. Having a redundant setup also might give some comfort. e.g. With two risers tied together at the top with a link, a slip of one might be saved by the other in level flight. Under high G it is not as certain, but better than nothing.

BTW if you are into high G manuevers, this might be a warning to see that all your equipment is top notch at all times and up to the task.

I'm going to have my ropes proof tested. This incident shows that there is possibly room for human error or materials defects even with the most careful operators. A proof test might reveal such a situation before there is a failure. Nothing in this life is certain, but the odds can be controlled to some extent.

Woody, my dad was an ironworker. I worked at the trade for a while too in my youth. Never learned to make cable eyes though.

Joe and Jacques: Don't beat yourself up over this. Be thankful no one was hurt and try to learn from the experience. Stuff happens.

Marty

[woodyking]

Your Dad must have been a great guy too. Ironworkers used to make all the rigging for all crafts, I was fortunate to have been taken under the wing of an old master rigger who worked at a choker table for many years. I spent close to a year as his right hand so to say, at the Savanah River Site in SC. Working with wire rope will put muscles in your hands and arms for sure, as well as some scars. I haven't seen a liverpool splice in many years now, probably not many who could do one, but I never saw one fail. The molly hogan is a much better to handle eye, without the barbs/tails to get you.

I'd think that most likely when a swage like we use slips, it's quick and all over, unless there was a couple inches of tail, which we know isn't the case. Having two with a space between them will show if there is any slippage, plus adds the factor that the second swage would also have to slip, as well as the tail between them would have to go through the primary swage. I'd bet that won't happen.

Check your rigging. Woody

[mignazito]

Woody:

My dad is gone now, but he lived to be 91. Though double swages might be a method, doing them right and checking them by proof testing seems to me to be a better way. In fact AC 43-15 suggests proof testing. I'm pretty careful with my swages measuring each one to see that they are in spec throughout, but I'm going to have them proof tested too.

Actually Kearny swages are fare superior to nicopress swages. I wondered why they are never seen in ULs. Then I checked the price of a Kearney swager. It is $3000 for the basic swager and another $300 for each set of dies for each swage size. Oversizing a nicopress cable and swage is far more economical.

Marty

[kilowatt]

Marty,

The crimp marks (rolls) look a bit unusual, compared to what we deal with. However, I couldn't offer any advice without inspecting the crimps more closely.

Most Nico's that we use, when used with the correct die, will leave very subtle compression ridges. You must remember that our full tension Nico's are end splices and we do very few "eye" splices.

Kilowatt

[mignazito]

Kilowatt:

The "end" or "stop" fittings do in fact look different. Since the loops hold two cables they have to grip both making the shape different. They also use multiple presses and the gaps between leave a ridge if you space then evenly. If you overlap the presses for a smooth finish you get big "lumps" on the ends. I prefer even spacing or as close as I can get as you see in the picture of my splice.

There is also a roll type finisher that compresses the entire copper swage into a smooth cylinder. The simple hand tool I have does an adequate job if used with care. I also gage the presses to make sure they are complete.

The Paraski press I checked was 0.050" oversize or not fully compressed. 0.500" vs 0.450" Not sure what that means about the incident.

Marty

[RandyV]

Well, I do not have proofing equipment but I do have a tractor and my machine weighs 400 pounds so I figured that I would at least see if I could lift the machine with each of the eight cables. I rigged up a clevis on the tractor bucket and one by one lifted the machine off of the ground with each riser cable. Definitely not a bona fide proof test but I certainly feel better.

Randy

[mignazito]

Randy:

Very inventive. That's more than the machine would ever see in flight, but less than an actual proof test. Making the best of what you have at hand.

Marty

[RandyV]

Marty,

Thanks, your approval means a lot. I usually take risks in stride but this incident got to me. The pre-flight checks seem very adequate and yet nothing showed up and the cable failed. We will have to wait for further investigation but there certainly may have been some corrosion occurring in the cable or connector. This failure occurred under conditions that were very mild compared to the worst loading that a cable sees during a few years of operation. I may conduct this lift test every couple of years just to make sure everything is OK.

Randy

[mignazito]

Randy:

The problem I see with Paraskis cables is that they use an opaque shrink cover that makes inspection impossible. I make my own cables and use a clear shrink wrap you can see thru to see if the cable has slipped. YHOu also need to gage the swages to see if they have been correctly compressed. For a 3/16" oval swage the dimension is 0.450" to 0.453" across the long axis of the oval. Insufficient compression would seem to me to be a concern about slippage. The one Paraski swage I picked at random from the dozen or so I had was 0.500" or about 0.050" oversized or undercompressed.

I would be inclined to either make a new set gaged and tested or at least strip off the wrap and gage them.

Your "proof" test is some comfort, but due to the critical nature of the design, you might consider going further.

Marty

[Skypilot]

Has anyone checked the failed sleeve to see if it was compressed properly. It appears the sleeve Marty checked was not. It may be that Paraski had a manufacturing problem and all of them should be checked. About a year ago we were making some new cables for our Parascenders. We took a 1/8 cable and put a standard eyelet and a single nicropree sleve (properly compressed). We then did a pull test on the cable to 2000 lbs. It did not fail. The cable is rated a 1760 lbs, but that is the minimum acceptable strength. On the Parascender cables (we have six of them) we installed dual nicropress sleeves on each end of all the cables to give a larger margin of safety. We dissagree with Woody that if one slips you would see the cable get loose between the sleeves. We believe the cables would remain tight until both sleeves slip but the likelyhood of both slipping is much more unlikely. It would still be difficult to determine a defective cable without testing them periodically. If you are going to test them why would you not pull them to rated strength. If they won't hold rated strength they should be replaced.

[RandyV]

Marty,

Right now I am pretty comfortable after lifting the machine with each of the eight riser cables. Once more facts are known about the actual failed cable we can decide what, if any, additional steps need to be taken.

Randy

[mignazito]

Joe Albanese and Jacques Fluery of Propulsion/Paraski will ask Barry for his cables to exmine them. They are sending a letter to all Paraski owners offering to exchange all single nicopress riser cables with dual nicopress cables free of charge. Apparently all risers after 2003 are dual swage types.

I don't know about you, but I think they are doing the right thing here. Essentially a continuing airworthiness program when a problem come up in the field. Under such a program they would not be obligated to replace parts free of charge, but they are going the extra mile and I applaud them for that.

Marty

[mignazito]

Skypilot makes a good point. Pull cable assemblies to in service rated proof test strength for the assembly. Pulling to higher loads BTW is not advised if the cable is going to be used in service. AC 43.15 has tables for cable proof testing. Pulling to higher loads than recommended for proof tests of cables to be used in service could compromise the strength of the assembly by yielding of the materials.

Actually pulling to lower loads can be justified based on the ultimate load limit of the entire assembly from wing to airframe. Most PPC wings are rated for an ultimate (proof) load limit of about 6000 lbs. Any component in the chain with higher strength than that is really of no benefit. e.g. A single riser cable out of 4 on such a setup could be tested to 1500 lbs and be more than adequate since it should NEVER see this load in flight.

BTW that load is well within proof strength of a 1/8" cable. Most PPCs use 5/32" or 3/16" cables with much much higher proof loads.

Gaging of the press compression is pretty reliable with occassional proof testing of samples made on the equipment used, but proof testing of each item before going into service is - well - "proof" of the strength of the assembly. Though rare, a hidden defect could compromise the assembly and your life. I would also suggest such proceedures for strap risers. They are man made items subject to failure like anything else.

[mignazito]

I went to my hanger today to get my copy of AC43.13 and check out the cable section. Interestingly enough it does not read exactly like I thought it did. Gaging is supposed to be done per mfg specs and there is not proof testing spec for finished cables. Only breaking strengths are listed for cable and various types of fittings.

It would seem then that any "proof testing" would be left to the mfg or owner if such testing is to be done. The AC and mfg information I have seen seem to imply that past tests have indicated that if the swages are made and pass the gage test for a proper swage they will meet the strength requirents of the cable and cabel assemblies. No proof testing of finished assemblies for use in the files appears to be specified.

Does this mean no testing should be done at all? No, but it appears from my asking a couple of A&Ps that it is not often done. It also appears there are not many places to get it done either.

Another interesting item surfaced in AC 43.13. The AC suggests applying red paint to the swage and cable loop where they meet on both side of the thimble . If the cable begins to slip thru the swage, the slippage will be revealed by exposed unpainted cable. Not a bad idea as well as cheap and easy to do.

If you do want to have your cables or strap assemblies tested, I suggest the wing ultimate load limit be "passed thru" to the cables and other components and used as the proof load for each component with it's share of the load.

After looking at my swages and some others I have on hand made by PPC mfgs, I'm convinced mine are going to be OK. I'm going to add the paint, gage all swages that have not been gaged where possible and go with what I have.

Marty

[Skypilot]

An interesting observation Marty. 43.13 also says that the proof test, if done should be to 60% of the rated strength. Another note of interest that hasen't been discussed are the quick links which attach the cables to the risers. They are typically rated at 880 lbs which is far less than the cables

[mignazito]

Quick links like Maillons are rated at a much lower % of ultimate strength than aircraft cables and other aircraft parts. If you rated a Maillon like say the cable, it's rated load would be much higher. Maillons are also rated in kg and if stamped 880 that is 880 kg which is 1971 lbs RATED WORKING LOAD, not ultimate or breaking load. The general rule is to use the quicklink stamped rating to at least meet the manuevering load limit and let the overrating of the Maillons take up the "slack" as it were. You can find the breaking strength in the Maillon catalog for reference.

I missed the part about the 60% in my reread. Perhaps that is what I thought I recalled was in 43.13, but imagined a table. Thanks for pointing that out. That's what this forum is about. Helping each other find the right answers.

Marty

[mignazito]

A further clarification comes to mind. The test should be 60% of the rated strength of THE ASSEMBLY and not the cable itself. Unless you are using Kearney swages on any cable or Stainless swages on stainless cable, the assembly is not rated for 100% of cable strength. Copper swages on stainless or galvanized cable are derated to 80% of cable strength. Most PPCs use coated stainless cable. I like to use coated galvanized because it is not only less expensive, but it is stronger. Also most PPCs use 3/16" cable so I estimate for copper swages:

Proof for 3/16" stainless is: 3780 X .8 X .6 = 1814 lbs
Proof for 3/16" glavanized: 4200 X .8 X .6 = 2016 lbs

You could also test to the wing ultimate load limit which in most cases is 6000 lb or less and for 4 cables would be 1500 lbs each if evenly loaded etc.

Marty

[mignazito]

More on this subject:

I have two cable swaging tools. An inexpensive bolt and wrench operated one and a fairly expensive long handled "bolt cutter" type. I bought the bolted one because I only planned to make a few cables for myself. I later acquired the long handled tool on E-bay for a low price.

The big surprise has been that the cheap bolt operated unit seems to make more consistent, even, correctedly gaged swages more esily than the long handled unit. In fact the only swages I can make consistently on the long handled unit are 1/8" ones and larger ones seem almost impossible to get right wasting a lot of expensive materials. The bolted unit hits them right on every time or nearly so. You do have to be careful with either one to position the sleeve correctly, but if you position them right the bolted unit comes out perfect every time while the long handled unit does not.

It may be the long handled unit I got at a low price is just no good because I see others on the airport making "good" swages with similar but different ones.

In any event I plan to only make critical swages on the bolt operated unit from now on. All he cables I am using or plan to use have been made on the bolted unit or are 1/8".

Marty

[Skypilot]

Another observation on the failed cable. The eyelet was still on the quick link and dosen't show any signs of damage (as it should if it was overloaded). Also the sleeve was covered with some kind ofa black covering which would seem to prevent inspecting the back side so if it started slipping it likely would go unnoticed. I still like the paint on the joint idea! We made new cables on the Parascenders because of Woody's help in identifing a design flaw that had caused some of the cables to break (thanks Woody). I believe I am going to paint them also

[mignazito]

Skypilot:

I tend to agree that this swage failed at normal loads or below and was the possible result of a poorly made nicopress swage. There is no way a properly made swage can pull out. Double swaging may be a solution, but I'm not so sure it is a good one. Two bad swages are not equal to one good one IMHO.

The opaque covers always concerned me. That is why I have used clear heatshrink tube to cover mine if I covered them at all. The paint however will reveal any slippage even if the swage and exposed cable stub are covered with an opaque cover. Covering the swage and exposed cable stub end is a convenience. The swage can rub on paints or parts causing damage and the "frizzy" cable stub end can cause minor injury when handling the cables.

Recently I ran out of clear heatshrink or cannot get large enough ones for 1/4" swages and have used some opaque ones or black tape on a few cables. I plan to paint all the loops at the swage junction however.

This incident was a wakeup call for me. I make my own cables and carefully gage them. If they don't gage right or don't look just right I scrap them and make new ones, but this incident concerned me somewhat.

Getting them proof tested seems to be more of a challenge than I originally thought. One aquaintance at the airport said I would have to send them to some place he mentioned in a far off state. There may be a boat marina. I need to look further. In the meantime I think careful gaging and visual inspection will do.

Marty

[wheelharp1]

Are these cables being discussed actually only 1/8" to 3/16" dia? The one that failed in the photo looks a lot larger in relation to the hand in the photo.

[mignazito]

Actually several single seat PPCs used 1/8" cables and most that use cables today use 3/16" which have a 3700 lbs breaking strength in stainless steel. ASAP Summit uses 5/32" which is still plenty strong enough for a PPC.

I have used a single 1/4" cable on each side (7000 lbs breaking strength in galvanized steel) in a couple of cases including my own Paraski. Perhaps that is a bit "gutsy", but if the swage is made right it should never break.

Cables are actually harder to make correctly than straps requiring a highly skilled operator. Skilled operators demand high wages. A special sewing machine and an operator who can be trained to run one are all you need to make strap risers so they have become the mode of choice for production operations.

Either method if done correctly is safe and effective.

For some one like myself who wants to make a few risers for himself, the tools and materials to make cable risers are more practical.

The cables in the picture as are most in use today on PPCs has a plastic jacket that makes them look much thicker than they actually are.

Marty

[wheelharp1]

The cables in the picture as are most in use today on PPCs has a plastic jacket that makes them look much thicker than they actually are.

Marty


It doesn't look like those cables have a jacket though...and shouldn't the jacket be removed from the cables before sleeves are crimped on? The only reason I'm asking is, I thought of having steel backup cables made...mostly for backup in case of an in-flight fire.

[mignazito]

You are looking at the bare end of the cable in the pictures where the jacket is stripped off to swage into the nicopress fitting and go over the thimble. I have seen and flown several Paraskis. They have all used coated cables as do most PPCs.

Obviously the jacket has to be stripped off to allow the copper nicopress to grip the cable securely metal to metal.

The coated or jacketed cables are simply more convenient for a PPC. The cables will not mar finishes and are protected from corrosion by the jacket.

You can also buy bare cable and slip a piece of 1/4" ID tubing over them before making up the final end.

Marty