Sump more than once

My airplane had been down for its annual inspection. The day after the annual was completed, I drove to the airport and did a thorough preflight inspection before a short maintenance test flight. I topped off the fuel, flew once around the pattern, and made sure everything was working. The next day, I flew the airplane 40 miles east to Riverside Airport (RAL). Both flights were uneventful.

The next time I flew, I ran the pretakeoff checklist and found no problems. On takeoff, the airplane accelerated and climbed normally. Suddenly, at 200 feet above the ground, the engine sputtered and rpm fluctuated from 500 to 700 rpm. Then just as suddenly, the engine stopped, and the rpm dropped to zero. I had practiced simulated engine failures over the years, in a variety of aircraft, but in my 40-plus years of flying, I never had this happen.

There was still enough runway ahead, so the engine failure happened in an ideal place—I was not over inhospitable terrain or a congested urban area. I immediately lowered the nose to maintain airspeed and glided toward the runway. I made a brief radio call to the Riverside Tower, saying, “Seven-Kilo-Yankee, engine failure, landing straight ahead,” and then I focused on landing. A few seconds later, I flared, landed, and was on the ground, rolling out at a high speed but slowing. I stopped on the ramp.

I attempted to restart the engine two or three times. It ran briefly each time, then stopped. So, I figured it was a problem with the fuel. I tried starting again, and this time it started and ran. I requested clearance back to the transient ramp and called my mechanic, Frank. I sumped the fuel again, checking for water in the fuel. The wings tanks showed no sign of water, nor the engine sump. We opened the oil access door, and I pulled the spring-loaded fuel drain tab on the top of the engine while Frank held a plastic cup below. We found our culprit: water in the fuel! There was at least a half cup. We continued to sump until there was no water left. Frank suggested I start the engine and run it at idle. I did, and it ran just fine. I shut the airplane down, and we checked again—no water. I started up and flew once around the pattern, then taxied in.

It had taken two flights before the water showed up during sumps, for whatever reason. I sumped the tanks before every flight, checking for water contamination, but it had not shown up. Another friend who is also an A&P suggested that perhaps rainwater had gotten into the tanks through the fuel caps on top of the wings. That can happen if the rubber seals and gaskets on gas caps become old and dried out.

My friend replaced the seals and gaskets on both fuel caps. His explanation for the engine failure was simple: Water can remain in the tanks, suspended, and then eventually work its way into the system during a flight. This is because of the mechanics of flying, including the jostling/movement of the fuel in the tank as you taxi, take off, and climb out, as well asnormal vibrations and turbulence.

If the tanks are not full, it’s easier for condensation to form in the tank, in the small empty space above the fuel, as the temperature changes during the day. This moisture can cause water droplets to form and contaminate the fuel.

John Mahany is an airline transport pilot and advanced instrument instructor with 47 years of experience in corporate flying and in Alaska. He owns a Cessna 150.