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.

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* I'm a mechanical/aerospace engineer (MS Caltech) and spent 5 years souping-up cars before college.

Thank you for posting this as it will trigger me to initiate this technique when suspect to possible water intrusion based on environment and situation.

This is interesting find, and if I remember correctly your airplane is stored outside, correct? I have found that in certain conditions, when parked in the elements, I have had an abnormal amount of water sumped from the tanks. This has only happened once or twice in the 30 some years of managing my plane. I have not tried to angle the plane to see if more water appears but I never typically have any water in my system unless I have been outside, in the hard rain, sitting for a period of time more than 3 or 4 days.

Good to hear you had a non-incident and no one was at risk during this episode.

Water proglems in the fuel
 

Hello Guys
after hearing Ernie incident , i would highly recommend to install the Monarch fuel caps, ,specially if the plane is parked out side, believe me it will safe you lot of troubles, out of 160 squawks i had during my pre buy , few of them were related due to water in fuel system ,as back engine was not producing enough power among others and it took lot of time and money to resolve those issue and i have installed these caps now.
Dennis

Nice job Ernie handling the emergency. I'm grateful all ended harmlessly. Very very fortunate indeed.

I would say water in my fuel is my biggest fear by far. So much so, I have managed to not have my airplane on a ramp in the rain. It sucks for sure. I wish I felt the same about my airplane getting rained on as I do my car but that has never been the case.

I've read this accident report several times on different occasions. One that sticks out in my mind is the C337 departing KPLK, Point Lookout (Branson), MO. The folks had been vacationing there and the airplane had been rained on during the week. Same exact scenario as your situation but if I recall correctly, both quit in that case. The airplane went off the end of the runway and down a steep embankment. It did not end like your case however.

Thanks for posting the information.

Ed

Dennis, good call on the updated fuel caps, as our aging aircraft continue to grow old any new and better device is a positive.

Let me discuss one issue that some folks have had that the new caps will not fix. In the service port of our aircraft is an overflow tube that collects small amounts of overflow and allows the fuel to exit under the wing. These small tubes are also suppose to drain any water that may try to collect in this service port when the aircraft is stored in the elements. Everyone should test these drains to be sure they are not broken or cracked. If they are compromised you will not know unless you try this test. Take a small amount of fuel and pour it into the service port, with the fuel cap on, while the bottom of the tube under the wing is plugged. Either have someone pour the fuel while you hold your finger under the tube under the wing or plug the tube with something that will not harm the pipe. If the fuel pools in the service port then the tube is sealed and working correctly. If the fuel drains from the service port then there is a crack or the tube is broken inside the tank. This is how the water intrudes into the fuel cell. I have personally seen this on my airplane and have read from others that this has happened. In fact it was determined that the Skymaster departing Point Lookout in Branson, MO had this very issue. Check your tank drains folks and if you have a problem be very careful when you leave your aircraft in the elements.

Please submit an FAA safety report.

https://asrs.arc.nasa.gov/?submit1=Continue

2 foot pipe cleaners mandatory
 

Having had some exciting moments just after I bought my 'thrasher, I realized the importance of those through wing drains.

Every time I was flying to Boston, the front engine would surge over Baltimore. I thought, "What is is about Baltimore my engine doesn't like?"

It was a thin bit of hidden water in the tank that took about 15 minutes in climb to hit the engine.

Ever since, I always intentionally drool a bit of fuel to make sure they are clear. If not, I always carry some 2 ft pipe cleaners bought on ebay, and clear the drains.

I consider blocked drains a no-go item until cleared.

-Hello thanks for the Tip ;pipe cleaner is next time in my ;list
Dennis

Heavy rain lately . Checked my drains for the scuppers that fuel caps are located in and by George bug had made a home in one. Scupper was full of water but new gasket on cap held the water out. Pipe cleaner used to open up again. Worthy of ongoing attention to drains with water works going strong lately.

After reading this I bought 4 toilet plungers and a tube of silicon. When the plane is outside during ANY amount of rain I put 4 small points of silicon on each plunger and place them over the fuel cap cover. before engine start my wife and I tip the plane up 2 times THEN sump the tanks.......it's simple too easy not too.
N2299X

A few years back, we had to park a few of our Skymaster on the ramp and never had a problem with water in the tanks except for our E model. The left aux would collect a significant amount of water after a rain. I changed caps, cleaned the scupper drains, did everything I could think of to try to figure out how the water was getting in the tank.
So one day I was fueling it and when the left aux was full to almost running over I noticed fuel coming out between the filler cap adapter and the tank. No sealer was ever there. So if you have a tank making water, you might want to check that