Thursday, 13 October 2011 12:20

This Happened to Me!

Engine Stumbles on Takeoff!

In my many years of flying I always like to think I’m prepared for a pilots worst nightmare, engine failure on take-off. Until it happens to you, one never knows just how prepared you really are! In this particular case, the engine came back and the pilot made a successful landing, but that momentary sputter really got his heart beating. The real question was, why did the engine stumble, then come back to life?

After countless ground runs, the problem repeated itself although again only momentarily. After endless hours of trouble shooting, nothing obvious was found? All the usual places were checked, carbs, fuel supply, ignition system, switches, p-leads what could it be? Eventually, by adding a specially modified float bowl with a sight glass to the two carbs, and after repeated ground runs the engine finally stumbled again and behold, one carb was out of fuel, its float bowl was dry???? After multiple disassemblies, inspections, cleaning, checks and double checks  nothing could be found wrong with the suspect carb……we were baffled. Again after multiple ground runs the problem repeated itself and again the float bowl of the suspect carb was dry, what the heck?????

Finally upon closer examination a very small flake of yellow witness paint(Torque Seal) was found stuck to the side of the small fuel chamber directly above the brass needle seat of the Bing Carb. This yellow witness paint(Torque Seal) is used to mark the fuel system banjo bolt fittings on the stainless steel fuel lines as used on a Certified Rotax 912F engine. The purpose is to allow the pilot or maintenance tech a visual reference if the banjo bolt is coming loose. The witness paint is added by maintenance personnel after they correctly torque the fuel system banjo bolts to spec. In this case, during routine maintenance, at some point a banjo bolt marked with the witness paint was removed, and a small flake of the witness paint was allowed to enter the fuel line were it eventually raised havoc!  This small flake of paint was just large enough it couldn’t fit into the small fuel inlet hole of the float needle seat, but rather would randomly block off the entrance of this hole shutting off the fuel supply. The small flake remained trapped in the tiny fuel chamber like a lion in a cage just waiting to wreck you day, a nice kitty when stuck to the side of the fuel chamber, a hungry mean cat when stuck over the fuel inlet hole!

What’s the moral of the story, “KEEP IT CLEAN, PAY ATTENTION”, the smallest oversight can have the BIGGEST consequences. In this case, even though a crash was avoided, countless hours of trouble shooting were undertaken at great cost and much anxiety to owner and maintenance personnel, all because of a simple oversight, don’t let this be YOU!


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