Hi Paul,

It is a 1969 Model C337D. Total time around 9000 hrs. Used to be N86439 if anyone out there knew it in USA! No idea on previous history of the cables. The problem is mainly a design one as the cable makes a sharp corner right my the long nipple and this is all around the back out of sight so only if your engineer uses a torch and missor and knows where to check will he see anything but in truth you'd be best to unmount that end of the cables and have the carefully inspected. We were lucky. Could easily have all ended in tears.

Flap Cables
 

I'm pretty certain there is a Cessna SB on these. The sharp bend around a smallish pulley is the culprit. The procedure for checking them is simple.

Take a rag, and wipe the cable. If it snags anywhere, you have a broken strand. If you have a broken strand on the outside, you undoubtedly have many on the inside. Waste no time, replace the cables. Both of them.

As others have pointed out, this should be part of the annual inspection that your IA performs.

The only way you can check these cables is to remove them at the bell crank. A flashlight and mirror doesn't usually show the frayed cable. I've attached a picture of where they fray. Hope this helps.

African 337,

Thanks! We have similar aircraft - we're flying a T337C. You are correct in that the only way to inspect the cables is to remove them. There are two per side which hold the flaps DOWN - these, of course, are the critical ones. There is also one cable per side to hold the flaps UP - these are much less of an airworthiness concern where a cable breaks in flight.

Once the four important DOWN cables have been removed for inspection, one might as well replace them. The cable and end connectors can be easily had, and then the only thing one needs is an A&P with a big swedger, and voila! four new fabricated cables for not much money.

I've heard of one operator of several 337s in Australia who does this routinely every year with his fleet of 337s.

I agree as well. Removal is the only way to inspect these cables. A visual inspection tells only a small portion of the story. It is better than nothing but probably not adequate.

Ed

Pics of JChronic's 1969 337D Inboard Flap Cable damage (x2) as found at 100hr/Annual Inspection - See attached.

As has already been noted by others you CANNOT see the affected areas of these cables with REMOVING them from the bellcrank. You MUST remove them for proper inspection. We replaced all 6 flap cables with new stainless cables and re-rigged the entire system per the service manual. The cables were tough to find but managed to find 5 out of the 6 we needed from 5 different sources. Had to have the last cable made/fabricated by Beechhurst Industries in NY (Ph: 718-468-1565). They can make most flight control cables under a Mil-Spec part number thereby eliminating the need for an STC or field approval....log entry only needed. The cost of the fabricated cable from Beechhusrt was the same as if I could purchase it from Cessna or other sources if it was available.

Let me know if anybody has any questions or needs any help.

- Tim/Aeromx

Great job!

Excellent photo's.

Ed

Thankyou to all who have contributed to this issue, I spent time with Don Nieser a couple of months ago in which he took me through the flap cable issue.

The photo's are a great help and add completion to understanding the issue at hand, will replace all wing cables regardless over Christmas.

Regards
David

If this was previously reported, please forgive the repetition. I talked with a missionary flyer last Sunday who reported a 337 crashing during this last year in Copan Guatemala (if I recall the location correctly). This was described as a fairly short, up-sloping runway - sounded challenging. It was probably a short field landing. Upon flap extension, only one flap extended but the other didn't. The aircraft commenced roll and impacted a deep crevasse just short of the runway. There were six souls on board; all survived, apparently un-injured or with only minor injuries.

The missionary, an extremely experienced bush pilot, blamed himself for not reacting faster in retracting the flap(s) to restore control.

The account I heard may have been in error regarding the failure sequence - perhaps the flaps were already extended when one snapped up.

A semi-happy ending for all except the unfortunate airplane. And a reminder for us all to be primed to quickly retract the flaps and add full power in case of un-commanded roll. This makes it important to have props forward and mixtures full rich when turning final, before extending full flaps.

Should we have the props forward and mixtures full rich whenever we extend any flaps at all? Or maybe do this turning base, instead of on final? This assuming we're close to sea-level flying a normally aspirated Skymaster.

Because some of the info on this thread did not conform with earlier knowledge, I spoke to Don Nieser about checking the cables.

It's true that a thorough visual and cotton swab/rag inspection may not detect a cable that may have a few broken strands, but we believe that it will allow you to make a determination on whether the cable is sound or should be replaced.

The fact that there are 100 or more strands and the typical design margin lead us to believe that a cable inspected thoroughly (visual and cotton swab/rag) and found to have no broken strands is good for continued service until the next annual.

I would add that it's not a bad idea to include this in your landing checklist: Flaps up immediately if aircraft rolls.

Ernie

For what it's worth, the reason I made my comment is because I've changed flap cables myself, I'm an AME here in Canada,. On one Skymaster, visually inspecting the cables before they were removed showed nothing. Once removed one cable had around 40-50% of the cable strands broken. There was no way of seeing this. With half the cable strands broken I question how much strength is left in the rest of the cable.

Tony, that changes everything. Question: it was a thorough visual, with flashlight and cotton swab/rag? And showed nothing, no fraying of the cotton? If that is the case, then I retract my prior message, and I'm sure Don would too.

Ernie

just a thought - i would think that cycles induce wear, base on that theroy low time and
less cycles would produce less wear. with one exception, some a/c had sheet metal screws that were too long and rubbing on the cable. year back i checked that and mine were. just replace the screw with a shorter one. it did not indicate any wear or broken strands; but that
was with 800.0 now it's 2000.0.

one could always drop the flaps well below the 160 maybe at the low end to reduce cable
tension and you really don't need them on takeoff, just a thought.

cost of the flap cables?
 

Thanks for this great info everyone. N2125X is just going in for annual and I will likely ask them to remove the flap cables for inspection based on this. Curious as to what the cost was for replacement cables?
Brian

As best I can tell, I spent $1,200.00 for all the cables and 10 hours of labor to do the job. Labor was another $770.00. So about $2000.00 for the entire job in September of 2009.

Ed