Flap Cable ACS
 

The ACS issued by the FAA about the flap cable failure that occurred last year has been posted on the Tech Data page............see attachments below
The ACS is a first step toward a potential AD. In it, the FAA asks questions of the public about an "airworthiness concern". The FAA uses the ACS to collect information and comments which may or may not lead to further action, such as an AD.

You are encouraged to comment on this ACS using this message thread. The FAA engineer who issued the ACS, and Tom Carr of CPA, will receive and are interested in your comments.

Thanks,

Kevin

Bogus!!!!
 

Hey Kevin,

What's the deal here? Your ACS sheet has no contact person other that Tom Carr down at CPA... this has no official standing, other than CPA fielding responses from folks who don't know any better.

I would suggest YOU and every other Skymaster owner read the posting that GMAS has placed on the UNO site for the real low-down on this. This is obviously another CPA endeavor/scam to collect information, and ONLY a CPA endeavor, with no official sanction, to make it appear as if CPA has the "pulse" of the 337. NOT!

I echo GMAs' response to this, in that no 337 operator should respond.

SkyKing

I don't subscribe to the CPA conspiracy theory. Anybody who drives a C-150 like Tom Carr can't be that bad. Unless he has become the unwitting puppet of CPA's demonic leader, John Frank, who schemes through the aviation world in the evil dark star Centurion.

It happens to be convenient for me right now. I'm going to pull it out, inspect it, lubricate it, and report back to CPA.

So, I run lean of peak and communicate with the devil.

Bawb

You can go here

http://www.cessna.org/flapcablesacs.pdf

and see the faa document. Looks to me like the respond to address is faa.
________
Starcraft ii replays

I got the document directly from Bob Busto at the FAA in Wichita. The first time it was posted on the CPA site, the contact information was removed. I did the same thing, so as not to flood the FAA guy with phone calls and such. As you can see from the bottom of the sheet, the idea behind these sheets is to gather information from aviation organizations and type clubs.

Anyway, you can follow the link in Ed's message to see the document with the contact information if you wish, and contact Bob directly if you would rather not use the web site.

The maintenance alert came directly from Bob Busto as well.

No CPA conspiracy, and genuine documents.

Bob plans to stop by our web site now and then to read the feedback, as will Tom Carr.

Kevin

I know Tom Carr personally and can attest to his extensive knowledge and love of the 337. His only interest is our safety. Things must be slow on Peter's site.

Flap Cable
 

The other day I was over at Don Nieser's hanger (one of them) and recieved some information from him that I would like to pass on to you.

First: Broken Flap Cable
I will attach a picture I took of the cable and bell crank on my aircraft (337B). It is the inboard bell crank just outside the boom. Using a mirror and light I feel you can inspect the cable very well.

Second: Long Inspection Plate Screws
Don also showed me a possiable trouble area with long screws in the inspection plate for the push-pull flap rod. When you inspect it the flaps are extened and the rod is a long way away from the screws, but when the flaps are up the rod comes very close to the screws. I believe a 3/8" blunt end screw will be long enough to hold the plate. I will attach pictures taken of my airplane (I had the problem).

Push-Pull Rod
 

Here is the first picture of the Rod, look at the shinny part where the screw was draging, it cut grooves in the rod, I will be watching it very closely.

Push-Pull Rod
 

This is the other rod. Make sure you take a look at yours and thanks Don Nieser.
Fred N358

Flap Cables
 

As flap cables seem to be a hot topic I can affer the following (my CPA post)
Just had a 337 arrive at the door with a broken left hand flap operating cable. The cable snapped just at the bellcrank and resulted in one flap up and one fully down on final, nearly causing a serious accident.
At the flap bellcrank in a 337 the cable takes a very sharp bend. We pulled the opposing operating cable even though it looked ok in situ, this cable when bent revealed that the heart strands were broken and also heading for a failure.
Cables look as if they have been there for a long time, dont have the logs at the moment so cant confirm that.
Suggest that operators of higher time 337's look at this area by undoing the operating cable at the bellcrank.
Would be interested if anyone else has experienced this in a 337, cable was gal and does not show signs of corrosion. As a precaution we have replaced all of the flap cables, removed and greased the bellcrank bushes, rod ends and flap rollers.
The picture on 337 site of Freds flap cable show that it is worn and could be heading for a failure. I strongly suggest that 337 owners of higher time (5k+) undo the cable at this location and inspect it. Because of the bend in the cable the wear is in the heart strand and inside of the cable and not visible in situ. Freds pic shows that the cable is not wound as tight in one location indicating that the heart strand could have serious wear and possible break. For those not up on cables these are 7x19 superflex 1/8 cable, this means the cable is made up of 7 bundles of 19 strands. At a sharp bend like this the middle or heart strand cops most of the wear and will eventually break, this accelerates the wear on the bellcrank side as now only 6 of the 7 bundles takes the load.

I can send photos that I sent to the CPA to show the cables if you are interested.

Fred if you are out there please e mail me to discuss your cable as I believe it is defective.

Best Regards
Kevin Swash
Chief Engineer
Aircraft Engineers Associates
Archerfield
Australia

kswash@aol.com

re cables
 

There are two cables of different sizes. Is the cable we are refering the larger or smaller diameter? Is it the followthru cable ?

We are in the middle of an annual now and I want to have the cables pulled for inspection.

Tnx

Bob

Cables
 

Bob
It's the small cable, flaps don't have follow-through cables, they just go from the jack-screw to the wing and back to the jack-screw. Hope this helps.
Fred N358 :D

re flaps
 

Fred-E

I am having the inspection done today. I saw another larger cable and thought it was a followthru. In this case a cable breaks and you really do have a problem. For some strange reason I had always invisioned flaps having a followthru cable in the event a cable breaks...

tnx for info

Bob

Flap Cable
 

Here is a little more info on our broken cable
p/n 1460100-7 Cable Assembly - Flap Actuator Inboard. 337 has one of these each side and it is the operating cable between the motor and inboard bellcrank. If you have stainless steel the p/n is -307. These cable is 1/8. This is the cable that fails. 2 per a/c

p/n 1460100-8 Cable Assembly - Flap Actuator Outboard. Again one each side and runs from the inboard to the outboard bellcrank. If you have stainless steel the p/n is -308. These cables are 1/8.

p/n 1460100-34 cable Assembly - Flap return. One each side runs from the outboard bellcrank back to the motor. If you have stainless steel the p/n is - 334. This is a 3/32 cable.

TTIS on this aircraft was 7504 hours. S/N 3370322

Pictures are attached of ;
Broken cable.
Location of broken cable (new cable fitted)
Opposing operating cable (close to failure this looked like Freds when it was in the aircraft)

location of break
 

See pic

pic3
 

this is the broken cable. NOTE it is 1/8 (big cable)

Flap Cables
 

FYIWed, Feb 26 2003

AD (Australia): Cessna
AWB 27-3 Issue 1, Cessna 336/337 Flap Cable Wear
Applicability: All Cessna 336/337 series aircraft.

Purpose: The purpose of this bulletin is to advise operators and maintenance organisations that excessive wear of the flap cable may exist in an area that is difficult to inspect during the periodic check of the cable in accordance with the maintenance manual. Excessive wear, corrosion or broken wires may result in failure of the flap cable, which can result in asymmetric flap deployment.

Background: This model aircraft has suffered a number of asymmetric flap extensions as the result of failed flap cables. The failure of the flap cable is caused by excessive wear at the inboard bellcrank, P/N 1462020-27. The wear location is at the tight radius bend on the bellcrank prior to the termination point of the cable. The cable wear is on the inside radius of the bend and is not noticeable without removal of the cable.

During one incident in the USA, the pilot lost control of the Cessna Model 336 on landing, but was able to recover control and successfully land the aircraft without sustaining damage or injuries. In a separate accident, again in the USA, the pilot of a Cessna Model 337 lost control of the aircraft on landing, after suspected asymmetric flap deployment caused by a failed flap cable.

In addition to the above two incidents, an incident occurred in Australia on 1 February 2003 where, on approach to land, the left flap completely retracted. Upon investigation it was found that the left flap operating cable P/N 1460100-7 had failed approx 1" from the left flap inboard bellcrank P/N 1462020-27. Further investigation revealed the right hand flap cable had broken internal strands. These were not visible until the cable was removed from the aircraft and carefully inspected. The cable has a severe bend by design at the inboard bellcrank location, which seems to exacerbate the wear and fatigue of the cable in this location.

The Model 336/337 Maintenance Manual requires a 100 hour inspection of the flap cable system. It is recommended that maintenance personnel treat the left and right hand inboard bellcranks (P/N 1462020-27) and all others in the flap system as "critical fatigue areas". A critical fatigue area is defined by FAA AC 43-13-1B as the working length of a cable where the cable runs over, under, or around a pulley, sleeve, or through a fair lead; or any section where the cable is flexed, rubbed, or worked in any manner. It also includes cable within 1 foot of a swaged fitting. As such, these areas require close visual inspection, which, in this case, can only be accomplished by complete removal of the flap cable so that hidden areas of the cable can be inspected for excessive wear.

In addition to the requirements of the Cessna 336/337 Maintenance Manual and the requirements of FAA AC 43-13-1B, operators maintaining the aircraft in accordance with CASA Schedule 5, must, according to Section 1 - The Airframe Part (2) (f);

"inspect the flight control system bellcranks, push pull rods, torque tubes, cables, fairleads, turnbarrels and pulleys".

A thorough inspection of the flap cable at the inboard bellcrank location will require complete removal of the cable in order to detect hidden damage.

Recommendations: Because of the criticality of the flap cables, and the difficulty of inspecting them in situ, the left and right flap cables should be removed and inspected for wear, broken wires and corrosion in accordance with FAA AC 43-13-1B, chapter 7, Section 8, paragraph 7-149(d) and the Maintenance Manual at the100 hourly or annual inspection, whichever first.
Reporting Action: If any excessive wear, corrosion or broken wires are detected, report it to CASA via a Major Defect Report (MDR) form (as required by CAR 52). In the MDR form, specify the exact location of the cable damage and include a sketch if possible showing the location of damage in relation to pulleys, bellcranks and other hardware. This additional information will allow CASA to assess the fleet-wide condition of the flap cable system and develop possible future action.

FMI: www.casa.gov.au/avreg/aircraft/AWB/27/003.htm

--------------------------------------------------------------------------------

I have been sick for a couple of days, and not monitoring the board. I just merged the three flap cable threads into one, to keep the information together.

I want to thank Kevin Swash for posting his pictures. Would it be alright if I posted those pictures on our tech data page Kevin?

I have some thoughts for you all on this subject.

I talked to several AI and A&P folks on this subject. The opinon was unanimous, and I promise I did not lead them on. Here is my best attempt to distill what I heard.

Bending these cables 90 degrees on the flap bellcrank (and other bellcranks) is done in many places, on 337s and other aircraft. 43-13 would seem to indicate that bending a 1/8" cable 90 degrees is not allowed, but the aircraft have been certified this way. All of the folks I talked to were sure that a very high percentage of cables that have been in service longer than 10 hours or so, and then are removed and bent in the opposite direction, will break as described in Kevin Swash's post and the FAA maintenance alert. Also, they believe that 100% of cables bent 90 degrees like this will not be serviceable for reinstallation once they are removed because they will be flattened excessively, and unserviceable per 43-13.

So, from what I learned talking to these folks, the following is my opinon, and my opinion only, offered for whatever it is worth to all of you. I am not a licensed aircraft mechanic. Here goes:

1.) If you remove the cable for inspection, you will probably end up replacing it. It will be unserviceable due to broken strands and/or flattening, even if it has been on the aircraft a small number of hours.

2.) If you do not remove it, you should inspect it carefully, using a tissue to detect broken strands. If you find even one broken strand in this area, you should R&R the cable.

3.) If an AD is issued relating to the problem, it should not be for removal and inspection of the cable, but rather to add a time change requirement for this cable. General opinion seems to be 5000 hours in service is a good maximum life. I have no expertise in that area, don't know what the number should be.

Comments?

Kevin (Mackenzie)

Also, to Kevin Swash, if you have time it would be nice if you could explain why you think Fred's cable is defective from the picture... I don't have an opinion either way, I am just curious to understand yours better.

Thanks,

Kevin Mackenzie

Flap Cables
 

Kevin to Kevin!

Pics no problem, use them where you please.

Your comments and questions
Bad design yes I agree but it works and has for a long time.
With regard to looking at the cable in situ if it has broken strands you want to know about it. It seems that the heart strands go first and these are not able to be inspected in situ. The cable in my pic looked like Freds in the mirror. This aircraft was 8 hours out of annual by a company that looks aftere several 337's.
1/ Broken strands. Just loosen the turnbuckle and undo the nut on the ends and dont bend it 90 if you are of the opinion that the cable will suffer damage from opening it up. Wiping a tissue on the outside of the cable in situ will not reveal the wear on the inside or heart of the cable. Wipe the inside to be sure.
2/ Must be removed to inspect.
3/ Nothing lasts forever and 5000 would seem a realistic life at the moment. Lets see what the lower time airplanes look like before we fix a life.
Why do I think Freds is defective?
Well look at the cable in the same location as ours broke and you will see that the cable has unwound slightly. This I would be concerned is due to wear and broken strands against the bellcrank and or in the heart strands.
Best to be safe than sorry!
Hope this answers all your questions.
Best regards
Kev

Kevin,

Thanks for taking the time to reply. My trouble, as an aircraft owner, is that if you ask a question of three aircraft mechanics, you end up with five opinions. I took you comments back to the folks I had talked to before. Some opinions were "that sounds right", others were that once the cable has been bent 90 degrees and stressed, the strands on the inside of the cable will be work hardened, and will break just from the act of removing the cable. These folks felt that removing and reinstalling the cable, especially repetitively each year, would do more damage than good, and they stuck with their opinion that if you remove it, you should replace the cable.

BTW, for anyone that isn't aware, the cables are relatively inexpensive, a couple of hundred dollars, but rerigging the flaps on both sides is many hours (perhaps as much as 20) of labor on a Robertson equipped P337 like mine. I don't know what the labor might be on a standard 337.

The exact science of aircraft maintenance...

Kevin

Heh KSwash
 

Hi Kevin, I'm in Adelaide
I also got the AWB and went straight to the LAME and asked how seriously he checked the cables during last annual I think I got the "all care no responsibility answer"
So I'm trying to get a better understanding of the situation with a few questions:
1. Your example is a pretty old serial number did the design or cable part number change during production
2. Did your cable crimp ferrule show any signs of corrosion
3. Did the cable or other components show any sign of corrosion
4. Is there any wear on the cable or components that can be contributed to multiple parts abrading each other
5. Are there any other visible signs prior to removing cables
6. Do you think this failure is related to
Atmospheric corrosion
Stress corrosion
Tensile stress
Mechanical stress ie. routing, or
fatigue

I suppose what I'm asking is this related to the earlier models, high cycle, corrosion or some other factor which will help me build a picture and maybe believe what I am being told by the maintenance guys


Regards ............. Wayne

reply flap cables
 

Kevin
I am no way suggesting these be pulled every 100 or annual that would be over the top. Pull it once now, fix it if they are bad then go fly a few thousand hours then take a look again.
If the heart strands have workhardened to the point that the cable will break when bent 90 degrees its probably time to change it anyway.
Cables are even cheaper if you find a shop that can manufacture them rather than buying genuine. We manufacture our own to sample and they sell for around $700 Australian dollars for the set of 6. (thats approx US$420) If any one local wants a set I can make from my samples here to save downtime.
twenty hours of labour sounds a little high cables only took us about 16 hours for the six. We took the oportunity to pull the flaps, grease the rollers, remove the bellcranks and grease the bearings, grease the rod ends and remove corrosion on the bellcranks and re etch prime. Total labour was approx 38 hours.
Wayne
1/My parts book shows the same cables all the way through 337 production without change.
2 & 3/There were no signs of corrosion in the cable or ferrule.
4/ No wear due to abrading, I believe it to be internal wear in the cable due to the angle.
5/ Slight visible signs in situ but very difficult to detect.
6/ Tensile stress perhaps. But good old fatigue definatly. At 7504 hours with an average flight time of 0.7 that would be roughly 22,000 cycles of the flap cable
Call me if you want 07 3275 3210 at work or 0419 182 206.

As I mentioned to a customer yeterday his 70 model plane with 7,300 hours at approx 150 knots has covered 1,400,000 miles. These planes are not getting any younger and need TLC!!

Reagrds
KS

If anyone is interested, I have new stainless steel flap cables P/N 1460100-307 and P/N 1460100-308 and the retun cable P/N 1460100-334. Also, I have most other cables for 337 and 0-2 aircraft. My prices are lower than any others.
Don Nieser
Commodore Aerospace Corp
6221 Commodore Lane
Oklahoma City OK 73162
405-722-4079 phone and FAX
405-503-4686 hangar cell phone
nieser.02.337parts@juno.com

flap cables
 

Just went thru an annual. Cables were removed and inspected. Both in Good shape. Total hours 2725. "P" model.

They were reinstalled and we are ordering two new one to be replaced at the next chance.

Bob

Flap cables
 

I have new Cessna stainless steel flap cables:
P/N 1460100-307 LH $60.00 each
P/N 1460100-308 RH $65.00 each
P/N 1460100-334 Return $65.00 each
Don Nieser
Commodore Aerospace Corp
6221 Commodore lane
Oklahoma City OK 73162
405-722-4079 phone and FAX
405-503-4686 hangar cell phone
nieser.02.337parts@juno.com

This reply goes to the board afther looking at the pictures Fred-E the rods for the flaps on my 336 have also been damaged by screws the one on the left wing has a grove of about 1 inch and a pin hole which has gone all the way into the hallow tub.

Should I Replace them before I fly againg?

Thanks


Francisco

Tin Man
 

Reminds me of a movie about ATC.... Land a million planes safely, no one says a word. One little mid-air, and they're all over you.

We hope that the information is valid, but based on things that have happened, and the information that Keven has presented, I think his observations are 100% accurate.
Thanks

Tin Man was a movie about a deaf guy who creates a computer to hear & speak for him (Timothy Bottoms).

Tin Men was about aluminum siding salesman, Danny Devito & Richard Dreyfus.

Pushing Tin was about competitive air traffic controllers, John Cusack & Billy Bob Thornton.

My plane's been in the shop too much. Is it obvious that I have too much time on my hands? ;)

Thanks
 

I knew there was Tin in there, and have seen all of them.
Thanks, it was Pushing Tin, which was actually quite humorous. Especially the scene when they stand on the ruway with a 747 passing overhead.

inspected mine and the push tubes showed signs of scraping on the inspection plate screw (only on the outter end) cables were ok. there is additional clearance on the inner push tube end and with shorter screws it has over an inch of clearance; however the otter push tube end there is very little clearance. the inner inspection cover on mine has the top center and top right screw holes adandones and small strips of alum. are riveterd in place to clamp on both sides were the tinnerman fitting were, so no rubbing is possible. however the otter cover does not and uses all screws. if you swap cover and use the inner on the otter you will have clearance (also swap the unused tinnerman clips on the otter area and place them in the abandon holes on the inner area. also make sure the screw are short enough to give clearance but ennough to hold. also i spray ac150 corrosion all over the interior every year so all cables and pulleys are always lubericated (two benefits in one application)
thank you for the pictures submitted it made it very easy to locate the areas, great job!!!!!!!!!!

Flap Cables
 

I've been changing cables on our 337's and thought ya'll would be interested in the results.
One with 3200 hrs 4 of the 6 were frayed -@ 6 to 8 strands
One with 2000 hrs 3 of the 6
One with 3000 hrs 1 of the 6
Kim

So what do you think, guys? If one were going to pre-emptively replace the flap cables, would one only replace the 2 inboard cables (which run from the motor to the inboard belcranks), or all six?

Paul

From the condition of the cables I've removed from our planes, I would change them all at @ 3000 hrs. You have to take them out to inspect them. When removing the cables I found it much easer to remove the pullies and leaving the cotter pins that keep the cable on the pully in place.
Hope this helps
Kim

Perhaps the cable strands are breaking because of the extra drag caused by the push rods rubbing on the inspection panel screws? Or, is there any extra stress on the cables for lowering the flaps at 140mph vs 100mph?

Personally, I think it is good to visually inspect. But wear items like this should be time/cycle limited. Aviation is only 100 years old. This is the first time in its history that 40-50 year old metal airplanes are flying with no manditory parts replacement times -- i.e., no contiued airworthiness instructions as newer airplanes have. I don't think Mr. Cessna ever envisioned that his airplanes would fly for 30, 40, 50, 60 + years, but they are. I asked Cessna, thru an email, what was the designed service hours/life of a 172; they never answered back. My guess is because they never considered it during its design.

This forum, and others like it, is a God's send. We are our own tech support, and are sitting at an historic aviation crossroad. That crossroad is: "How long can you fly an airplane before it just falls out of the sky?"

Old thread, new broken cable.
 

All, during my 337 refurb project, we just put the wings on and were routing the flap cables when I discovered my inboard flap cables (specifically called out in the above) also showed broken strands exactly where this issue was identified. I strongly recommend folks look at this area next time their aircraft is opened up or has the rigging touched.

1460100-7 is the part number.

Guys this is a really old thread but all good

I replaced my flap cables back in 2010 and found several with broken strands that could not be seen until you removed them and bent the cable back.

The reason for broken strands is not load related, but has everything to do with the bell cranks. There is a sharp 90 degree bend in the cable when the flaps are actuated and this continued bending to this extreme force will eventually break the strands. I don't know if these cables would ever fail because there are so many strands that are still attached. However I had my cables out for inspection and had new ones in stock so why not put the new cables in the wings. Personally I think it would take a long time for the good stainless cables to fail. The failures in the field have been on older 336 and early 337 that had the non stainless steel cables and were in high humid environments. It's just peace of mind to check these but be sure to have new ones on the shelf so once you take the originals out you can replace with new, don't put the old ones back in service.

P337 stainless flap cables
 

I'm trying to find as much info on this issue but can't really find it. Does the stainless flap cables have less of a chance for for strands breaking over regular steel cables? Have almost 5000 hours on this P and thinking about at least replacing the two. We have stainless already.

Most cables today are Stainless Steel and that is because of corrosion not broken wires or strands. I would venture to guess that every Skymaster out there has probably got a broken strand or wire and this is not from stainless steel cables but from the design. Because of the radical bend in the design this is what breaks the wires or strands. Back in the day of 336 and maybe early 337 some failures of flap cables could have been from corrosion. With the stainless cables this should be eliminated. For my own peace of mind, I replaced mine just to know for sure what kind of shape they were in. Just have new cables ready to install because you won't want to put the old cables back in once you see the broken wires or strands