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IMPORTANT ALERT -- Engine quits on takeoff due to undetectable water in fuel
I will give you details in a moment, but here are the findings:
Sumping the fuel tanks and finding no water DOES NOT mean there is no water -- there can be enough to make your engine quit in the middle of your takeoff, and the only way to find out is to lower the tail of the airplane all the way to the ground, raise the tail back up so the airplane is level AND THEN sumping the fuel. About a month ago, on takeoff, the rear engine quit on my 1977 337G. No stumbling, just quit. I was about 20 - 30 feet above the runway so I shut down the front engine and landed without incident. On the ramp I did some diagnosis*, including running the engine at full power, and found nothing. Given the gravity of the incident, and because the Annual was nearly upon us, my mechanic started a painstaking weeks-long effort to find the problem. The injectors were cleaned, the fuel pump checked, all fuel lines checked, and although we felt it was a fuel issue, we also compression-tested the engine and checked all spark pugs and wires. Still nothing. I then called the big guns: the head tech at Certified Engines, the service rep for Continental Engines in Miami. He checked everything, put the fuel adjustment meters/gauges on the engine, and found nothing. On a hunch I wondered if there may have been water in the fuel tank that doesn't show when you sump -- and doesn't reach the engine -- when the aircraft is level, but reaches the fuel line to the engine when the aircraft is in its tail-low angle of attack of take off. The suddenness with which the engine stopped, without stumbling, was a strong indicator that this was a fuel issue. And my hunch was also borne of the fact that water had been accumulating in the bowl of the fuel cap on the right wing, from where the rear engine is fed. To test the hunch, we sumped the right-wing fuel and found no water, just as I had found no water on my ill-fated takeoff. We then lowered the tail of the airplane until the plastic fairings at the bottom of the rudders were nearly touching the ground and after about 15 seconds raised the tail back so the aircraft was level again. When we sumped again we found a significant amount of water. Using a regular fuel tester ASA P/N 13-18464, I must have taken out 4 - 5 tubes full of water, and another 4 - 5 tubes with diminishing amounts of water. I flew the airplane today, all was well, and I have no doubt that this is what caused my engine to quit. If you have any issues with water not properly draining from around the fuel filler ports, or any doubt about water in your fuel, lower the tail of the aircraft before sumping. _______________ * I'm a mechanical/aerospace engineer (MS Caltech) and spent 5 years souping-up cars before college. Last edited by Ernie Martin : 06-11-19 at 06:35 PM. |