Yesterday, while climbing from a departure, I noticed my 170A was yawing left. No wind to speak of. Ol' 9291A has always flown straight and steady. The immedate landing was uneventful. Long story short, I found the rudder cable had slipped off the front pully and lodged between the rudder pully and aileron pully. Loosening the pully assembly was necessary to pull out the bound cable. The cable was reset on the pully, all tightened, and all is functioning as should.
Question: Could one of my less than desirable landings caused the cable to 'slap' off the cable? Or is there some other problem that could cause this issue to happen. I wouldn't think I am the only one this has happened to.
That's a very serious issue. See 49 CFR 830.5(a)(1), "Immediate notification." (of the NTSB). It needs to be tracked down and solved by a qualified mechanic before flying again. IMHO.
John Renwick
Minneapolis, MN
Former owner, '55 C-170B, N4401B
'42 J-3 Cub, N62088
'50 Swift GC-1B, N2431B, Oshkosh 2009 Outstanding Swift Award, 2016 Best Continuously Maintained Swift
azmuth1 wrote: I found the rudder cable had slipped off the front pully and lodged between the rudder pulley and aileron pulley. ... .
Question: Could one of my less than desirable landings caused the cable to 'slap' off the cable? Or is there some other problem that could cause this issue to happen.
John,
Was the AN 380-4-5 cotter pin (#10 in the illustration below) in place?
What happened on your landing(s) that makes you think it could cause a rudder cable to come off a pulley? Did you have to jam the rudder really hard? Do you remember which rudder or direction was applied? Have you checked the tension on the rudder cables? Are they lubed? Could the rudder cable have damage or excessive wear elswhere that becomes an issue with abrupt or hard application? This damage could be in a location that is hard to find. At the very least, you should have the entire rudder cable circuit inspected. I agree with John Renwick in that you need to have a qualified aircraft mechanic to check this out before further flight. This is the kind of problem that could have serious consequences and I am not talking about a simple loss of control on landing. Good job on getting it back down safely and hope to hear what, if anything you find because we will all benefit should you find a "smoking gun".
A couple of more thoughts regarding John Renwick's observation that this event is reportable to the NTSB. It is and you should consider getting in touch with your local field office and give them a report. You will not get in any trouble for it. They may refer it to your local FAA office for an investigation. The point is to get a serious issue like this into the system so the cause (or probable cause) can be determined and the information spread to prevent future occurrences. Think of it this way: If there is a potential defect in a Cessna 170's rudder control system based on a bad cable (defective part), maintenance issue, etc. this information needs to get out to prevent future accidents and possible loss of life.
In reality, the NTSB is a busy organization and is understaffed. I recall an incident a few years back where a King Air had a total loss of aileron control and the pilot barely made it safely to the runway. The operator was unaware of the NTSB requirement and did not file a report for nearly a month. He did not get in trouble and the NTSB did not even assign it an investigation number because the cause was identified immediately. The last mechanic who installed the aileron missed the recieving nut when he or she attached the hinge bracket to the aileron ( a known hazard in Beechcraft products). There was nothing for the NTSB to investigate. The problem was handled through submission of an FAA Malfunction and Defect Report (M&D) which gets the word out to mechanics and IAs and informs (or in this case reminds) them of problems that can result in serious accidents or incidents. I believe as pilots and mechanics we have a responsibility to participate in this system because it can and will save lives.
This is probably what needs to happen in the case of this cable slipping off its pulley. The cause needs to be identified (if possible) and the information needs to be disseminated. At the very least, a qualified mechanic needs to investigate it and file an M&D report with the FAA.
I've not heard of this happening in over 10 years here at the forum so I would say the cable coming off the pulley is not a common occurance. Look at this very hard.
BTW when replacing the return springs I had the occasion to loosen these cables, flop them all around and then just tighten then up and they all were still in the pulleys. They just don't come out for no reason.
CAUTION - My forum posts may be worth what you paid for them!
Bruce Fenstermacher, Past President, TIC170A
Email: brucefenster at gmail.com
Only 3 possibilties here, in this order;
1. Missing or severely bent cotter pin
2. broken pulley. I've seen the lip broken off on some which could allow the cable to come off in the right (wrong?) position
3. Someone installed a smaller pulley at some time, either not paying attention, or possibly to "correct" another problem, such as a shorter turnbuckle at the rudder bell crank.
There is just no way for the cable to come off the pulley if all correct hardware/parts are installed and in airworthy condition
John,
The illustration I copied above was from the C-170B IPC. I see now that the IPC for the A model is more enigmatic. It says to refer to fig. 46 for the details of the pulleys (item #2). But in looking at fig. 46 (which is for the aileron control system) it is not evident to me where the cotter pins are for the forward rudder pedal pulleys. I can see that it would be easy to miss attaching cotter pins here if you only referenced the C-170A IPC.
Model A rudder system.jpg (21.35 KiB) Viewed 6050 times
The rudder cable and aileron cable pulleys are side by side, (one of each, on each side of the inside of the tunnel), and one cotter pin is used for the pair (one cotter pin on each side).
Just a note; the cotter pins are very difficult to remove and reinstall because of their location. When replacing cables, it's easier to remove the one bolt for each pair of pulleys, remove or displace the pulleys upward, to replace cables. The problem with trying to remove/reinstall the cotter pins is getting them unbent for removal, and new ones bent on reinstallation, so they don't slip out. I can imagine the frustration of this task, coupled with a poor attitude, a mechanic getting the new pin slipped in, and only partially bent, if at all, and saying "to H*LL with it".
To answer a couple of the questions; I did suspect a rudder return spring, both were functional, not broken; though the spring on the pilot side is newer and had been replace prior to my purchase last year; maybe this a place to look into to see if the cables were loosend and re-adjusted correctly according to the owners manual. As for the cotter pin question; I can see no place for a cotter pin or evidence of a place to install one. Looked from every angle. If there is one, it is well hidden from site from above, below, and sides. Yes, I will have a A&P look into this.
yup, there needs to be a cotter pin. it's only function is to keep the cable from jumping off the pulley, which as you've found is kind of important. I hope you figure out the problem quickly so you can feel good flying again.
'56 "C170 and change"
'52 Packard 200
'68 Arctic Cat P12 Panther
"He's a menace to everything in the air. Yes, birds too." - Airplane
The cotter pin is the only device which keeps the cable positioned on the pulley and MUST be installed. I've seen an instance where the cotter was passed thru only one side of the pulley-bracket...and it's opposite (receiving) hole was missed...yet the pin bent and presumed to be properly installed. Of course, it was not and the cable was held onto the pully only by cable tension (which is fairly insignificant in these rudder circuits.)
Azimuth1, if you look closely you'll see a small pin-hole in each bracket side to receive the cotter.
Since this is obviously an installation-error, (and perhaps an inspection/mx error) a Defect report is all that should be necessary. I don't think a report to NTSB is appropriate for such a failure since it's not a material or design failure.
'53 B-model N146YS SN:25713
50th Anniversary of Flight Model. Winner-Best Original 170B, 100th Anniversary of Flight Convention. An originality nut (mostly) for the right reasons.
azmuth1 wrote: As for the cotter pin question; I can see no place for a cotter pin or evidence of a place to install one. Looked from every angle. If there is one, it is well hidden from site from above, below, and sides. Yes, I will have a A&P look into this.
John
The cotter pin hole is located at the 6 o'clock position, in flight level attitude. I have one with the firewall removed, and would take pictures, but I've never been able to post them.
Moderators note: Del can fix anything...(and notice the quality of his restoration-work)....
but posting pics is beyond him.
Here's his pics: Note the cotters installed thru the brackets at the bottom of each:
Del sent pictures that were a great help! The cotter pin is broken. It must have been the original...not a pretty site...old rusty and bent. A little raskel to remove. The other pully side didn't have a cotter pin at all. Some of us are on the edge and don't even know it. I want to thank all of you for input. Every one of you contributed with important help.
Or is there some other problem that could cause this issue to happen. I wouldn't think I am the only one this has happened to.
