5-Year Rubber Replacement may be Dangerous to Your Health!

[drdehave]

“Mission Control: We may have a problem.” At least, it is starting to look that way to me. Admittedly, my evidence is circumstantial, anecdotal, and involves a small sample size, but, when it comes to aircraft safety, isn’t that enough to generate some mitigative action? Maybe...

Here’s the basis of my anecdotal evidence: I am in pretty close, regular, contact with five (myself included) Sting Sport owner/pilots. Four of the five, including me, have now completed their 5-year rubber replacement. Three of those four have now had serious fuel-system-related issues a very short time later, as follows:

A. In my own case, a couple days later, I began intermittently losing power during full-engine-loading at take-off (There was no sign of an issue during the 4,000rpm run-up.). This resulted in three forced returns back to the runway and one very low-level go-round that I almost didn’t make; I was, in fact, seriously thinking to pop the BRS lever when I finally made the runway. The culprits were found to be two small pieces of unknown debris in the starboard carb bowl, getting sucked up into the jet orifice during full (only) manifold pull. In addition, at about the same time, I serviced my gascolator, finding more debris than detected ever before during my previous 550 hours of flight.

B. One of the other owner’s had a case very similar to mine (with no sign of an issue at run-up), except the offending culprit was one very small piece of rubber found and removed from the carb bowl on the port side of the engine.

C. Case number three was a little different and involved sudden, very serious rough-running and loss of power during straight and level flight–with no previous rough-running ever before. The owner/pilot was told by his A&P that “a cable had slipped, putting the carbs out of sync.” Nevertheless, that owner remains strongly suspicious that it may well have been some fuel-system contamination issue related to the rubber replacement.

So that’s the anecdotal evidence, folks. Now, I think most of us will agree that we have, for the most part, “warmed” over time to the need for, and benefits of, the 5-year rubber replacement. But these events suggest the need for some serious discussion about “Best Management Practices=BMPs” to be followed during this endeavor–to prevent fuel-system-contamination issues, which could be quite hazardous to a flyer’s health, to say the least!

To that end, I have begun (#1-3) a BMP list below. I would like to add to it over time, eventually developing a more comprehensive list that mechanics can consider and owner/pilots can refer their mechanics to (if they haven't already thought about the subject) when the issue of 5-year rubber replacement rolls around. My background is as a biologist–not an aircraft mechanic. So, I’d like the rest of you–and especially the real mechanics–to chime in with your thoughts. If such BMPs already exist someplace in writing (If so, I couldn’t find them.), let's post them up and dispense with my little exercise. Otherwise, what are the specific BMPs that you can think of that could and should be added to the list I started below?

BEST MANAGEMENT PRACTICES FOR PREVENTING FUEL-SYSTEM CONTAMINATION DURING THE ROTAX 5-YEAR RUBBER REPLACEMENT:

1. Bulk fuel-system lines should be stored only in clean, enclosed containers and never open and exposed, such as on a shelf or the floor; and
2. When old lines are removed, all open fuel-system orifices shall be capped or plugged, immediately; and
3. New fuel-system lines shall be double-flushed with air and/or gasoline just prior to installation; and
_____________
4. Cut all hoses with only the sharpest of instruments, to avoid ragged edges and cutting debris; and
5. Clean and flush (air) any fire sleeves through which fuel lines are to be inserted AND consider capping the fuel lines during the insertion process; and
6. After fuel system hose replacement and engine test-run, shut down, remove fuel hoses at the carbs and drain some fuel through for flushing action, with particular focus on the 1/4-inch line from the fuel pump.

...list to be continued..with any additional input other posters provide. This is not a "must do" list for anybody; it is to get folks Thinking....--R

[roger lee]

The 5 year Rotax rubber replacement is in full swing and has been for over a year. If you have an SLSA you need to make sure the 5 year rubber replacement gets done. Flight Design had over a hundred to do last year alone and another hundred to do this year. There has been a few issues with debris in the carb bowls after the change and here's why and a quick look at the fuel system in general.
Everyone who replaces their fuel lines have to cut the length they need to fit their plane. We tend not to use nice super sharp scalpels and cut our lines with knives or scissors. These tend to leave very small sometimes hard to see ragged ends with a piece of debris just waiting to get ripped off as it slide over a metal fitting. Then some of us (like you're supposed to, push the fuel hose through a piece of fire sleeve. This can gather some of the fire sleeve liner into the hose. Then we push the fuel hose over a barbed fitting which breaks off these little particles of hose. None of typically blow the hose out or flush it out prior to this installation. After start up you should be doing a carb sync. There is not enough flow or turbulence within the bowl at this time or enough particles to cause an issue so off you go to fly. Now we fly and we are at full throttle and now you have enough fuel flow to get these particles moving and enough carb bowl turbulence to get then in the fuel flow and headed up to the main jet. This causes some fuel starvation. Most people just loose rpm and never actually shut down.
The fix is to make sure you use something very sharp and clean to cut the hose, then flush or blow out the fuel line before the install. Then after the complete plane is done then pull the fuel hose off the carb and turn on the fuel or fuel pump and drain a little fuel through the system.

Depending on your system setup your fuel system route and filters should be similar to this:
The fuel out of the tank goes through a fuel filter, then through a gascolator with a 100 micron very fine mesh screen ( those particles can't get by here), then up to the mechanical fuel pump which has another internal fine mesh screen ( can't get by here either), but after that it is a straight shot to the carbs.
The debris some of you have found should have come from the 1/4" line off the bottom of the fuel pump that feeds the carbs. All fuel lines should be cleaned out during install, but this is the one that is putting the debris into the bowls. This one after installation should be flushed with a little fuel. Over crimping the hose with a clamp can also cause mechanical damage on the end of the hose where it contacts the metal barbed fitting breaking off debris.
I have done 23 hose changes. I had two that made the engine cough upon a test flight. These were early on and I have now adopted better fuel line installation techniques and no more problems.


The bottom line is to use better and more sterile techniques when we install fuel line.

[drdehave]

Roger, thank you! See if #4-6 that I added to the original post, captures additional guidance you just provided.--R

[roger lee]

4&6 look spot on to me. These things made me change some of my procedures.