Hose Debris - The Most likely and Common Cause

[Safety Officer]

Just an FYI,

 

 

I cringe at the thought of bringing this subject up again because it takes on a life of it's own and ends up going down the wrong path, but here goes.

 

After a year's worth of looking at carb debris issues and cutting hose open on engines that had a lot of rubber debris I think I have a reasonable handle on the cause.

 

Plain and simple: OVER CRIMPING or over tightening of the clamp.

 

On all the hoses I have examined the hose between the fittings have all been in good shape. The problem areas have been at the fittings. The hose has a thin liner of Teflon or other inner material. If crimped too hard on a barbed fitting it cuts this layer and then pieces can become dislodged and fuel especially with ethanol can now get under that lining where fuel was not meant to be. Make sure your mechanics have a handle on the type of clamp and size that they will use and do not over crimp or over tighten clamps. The proper size Oetiker clamp can only crimp down so far. Any type of screw clamp or even the Band-It clamp if used on the fuel hose itself can cut the inner liner when over tightened.

 

It is obvious that barbed fittings can work if used properly because they are every where in engine use in the world, BUT due to lack of education on fittings, hose and proper clamp use there can be cause for concern over debris that will cause an unwanted and unexpected rpm drop in flight.

 

The best fix would be for FD to stop using barbed brass hose fittings and use AN fittings with a smooth shank and a flared end which would only be applicable on the 912 carbureted engines. The new Rotax fuel pumps uses these fittings. It would be nice if FD would issue an LOA so anyone that wanted to switch to the AN fittings would have that option.

 

Back in May 2012 Rotax had a service Alert out for some Gates Barricade hose on the bottom fuel pump hose that was actually a bad batch of hose. This was from the Rotax factory and I do not know if any was from hose reels in the US, but that time is long past.

 

Here are a few pictures to show you what over tightening a clamp can do. This hose had a Band-It clamp installed. The long smooth cuts where from a box knife opening the hose. These are only one hose I have seen and some are worse.This particular hose produced 14-18 fairly good sized particles in the carbs. All capable of blocking the main jet.