I've been thinking about things like this for my build and I'm tending to shy away from adding items that can produce toxic fumes during a cabin fire. PVC, CPVC are high on the list of things I will avoid using for this reason.

I'm thinking if you have a cabin fire your day is not going to end very well, with or without toxic fumes. It is better to start off with cockpit items that don't or resist catching fire.

Fair enough but 1. PVC and CPVC still don't meet your criteria and 2. When they do burn they give off toxic fumes that can debilitate you quickly, which could be the difference between a successful, if rough, landing, and a mid air loss of consciousness and death.

PVC in the Cabin
 

I work in the airplane mod business. PVC is not allowed in the cabin for the reasons given. We don't install wire harnesses that have PVC content in the jacket which was difficult at times to find suitable work arounds but not so much any more. Nobody wants a fire in the airplane - it's a bad day for certain. But don't make a bad situation even worse if you can avoid doing so. Do some research on content of materials before you place them in your airplane. I am especially wary of material in proximity of the firewall or near high current conductors. Avoid PVC content please.
Safe flight to all.

Suggested material?
 

I hadn't thought about the fire issue because I'm not encasing something electrical, but does make sense to avoid materials that would have issues with fire even though they are unlikely to be the source of the fire.

Any suggestions for light weight, sturdy, flame retardant tubing?

Good point Ben. Taking that advice, I will remove the piece of conduit from the front of the wing spar to the rudder cables. My interior side cards and arm rest are foam covered in leather and if there is a fire, they will likely burn, so the conduit behind them will not be the issue at that point.

To help with fire, I am installing cork on the floor under the carpet. I tried a test with my map gas torch and it is very good at keeping heat away. The aluminum floor will melt pretty quick, but the cork could give me another minute or so. I am debating putting the cork on the engine side of the firewall too. I have not found a way to fasten it to the firewall I am comfortable with so still thinking about that one.

There's no way I'll have a primary flight control system that I have to disconnect to inspect. That's just asking for something to go wrong, especially if it's at all awkward to access.

On the other hand, a mirror and flashlight might be sufficient to inspect the cable.

Dave

How often are the control rods inside the wing checked? How about the rod under the seats that control the elevators? They are protected by the wings and seats, so we are all comfortable checking the ends. I would say a cable inside a protective conduit is about as safe from damage as anything else on my plane. I don't have to worry about snags or damage because it is protected. Having the cable inside the conduit eliminates the need for inspection at each flight. Both ends are visible at all times. That is no different than any of the other control systems on the plane.

Are you going to pull the cables out of the conduit at every condition inspection? Those plus the pushrods deserve a very careful inspection once a year. I would not want to be disassembling any control system parts unless I were repairing something.

You can inspect the ends every time you get into the plane or walk by the rudder. They are not covered in any way. Because of a suggestion about fire and smoke, I stopped the conduit at the front of the wing spar, so the last 2' or so in the foot area is always visible.

If you want to inspect the end and entire cable, you unbolt the end from the rudder pedal and pull from the rudder area. The entire cable - with the end still attached can be inspected by just pulling on the cable. You would have to take the plastic hose where the cable passes from the fuselage out to replace the cable. To re-install, you can push the entire cable - with the front end attached through the conduit all the way to the front of the plane. Try that with just the plastic snap rings.

Im not suggesting anyone do this. It obviously inst needed with the thousands of planes flying just fine with the snap rings. I did it on my plane because I can and believe it is a better solution for me.