Gary Rode

Docket No. FAA-2008-0685 Directorate Identifier: 2008-CE-039-AD Background: A one mm, tighter fitting hose clamp; might be necessary to eliminate the possibility of the new, Metal Fuel Fittings from leaking in the Stemme Motorglider. Controversy: Reduced Clamp Size, or Correct Fitting Diameter? Retrofitting All clamped components is unnecessary and introduces potential damage (especially to plastic Check-valves). Analysis: 1) The leak occurred, because the New Karcoma Fuel Fitting (T-connector) is smaller than the Fuel Hose Diameter: 7.13 mm Connector Hose stem, within a 7.5 mm Fuel Hose ID. 2) The New Karcoma T-connector is nearly one mm smaller, than all of the other Fuel Fittings (8 mm). These other Fittings do not need a tighter Clamp. 3) Mechanical removal of Mold Lines, could further reduce and potentially flatten the Hose Stem Diameter. Mold Flash left intact, might imprint hoses. Used & re-positioned Hoses on these connectors, would probably leak. Old Hoses have memory & drepressions! 4) The New Metal T-connectors are made of Zinc, a very reactive metal with acids (Non-stop White Rust contamination). The Original Plastic fitting (Norma YS 8, yes it's 8 mm) failed from Acidic Corrosion. (Fuel Fungi) 5) Most importantly, while the hose is being effectively pinched (to accommodate these smaller metal fittings), what happens to all of the other, larger Fuel Fitting Components? Would the Fuel Hose integrity be compromised? Over-compressed by the fear of future fuel leaks? 6) The Fuel Fitting OD should closely match the Hose ID. Stretching the hose (tighter connection) establishes Tensile Stress, which in the presence of Acid; will lead to Stress-Corrosion Cracking. Failures have been observed in 90 degree Hose-bends (& connected Hose-ends). Recommendations: Stemme has received many complaints, regarding the Karcoma T-connectors. Down-sizing the Clamp-size is only a Band-aid. A long term solution, would be a Superior Connector, Properly-sized, and Corrosion Resistant. Fortunately, a Stemme Pilot (Julian Fuchs) found the perfect 8 mm (5/16) Stainless Steel (316L), injection-molded T-connector source in the USA... Eldon James: http://www.eldonjames.com/PDF/SS.pdf These Connectors are neither Machined, nor Welded. (No SCC) This proposed Clamping AD is contrary to Recommended Clamp Selection: The middle of the clamp range should correspond to the applied Hose OD. The New Clamps (P/N 10M-181, 14.5 mm max.) fit so tightly, that improved Fuel Hoses (like Goodyear's 8 mm, Type 3) could not be used (without significant difficulty/damage?). http://www.eldonjames.com/html/ClampGuide.html References: The Karcoma Connector (30-0554) is under-sized, poorly constructed, & inaccurately advertised (as 8 mm): http://www.karcoma.com/en/products/overview/components/hoseconnections.php Other 8 mm Stemme Fittings: Plastic (POM) Check-valves, Fuel Filters, Fuel Pumps, Fuel Cocks, Water Separator, & Differential Fuel Pressure Sensors. The New, Metal Karcoma Fittings are dangerous, and this proposed AD will insure the threat spreads like cancer! The only real sealing surfaces, are the Hose Barb & the narrow, Inside Shoulder. Gary Rode