Rain, Cold and Fuel Caps

They say every accident is the result of an unlikely chain of events: On a Friday afternoon, a student and a flight instructor prepared for a flight lesson. The flight school’s fuel truck was servicing the airplane as the two began their preflight inspection. The lineman, seeing that the pilots were present, filled the fuel tanks but left the fuel caps off. Later he said that he had left the caps off on purpose, thinking that the pilots would want to verify that the tanks were full during the preflight inspection. Then, for some reason (possibly weather), the pilots decided to postpone the flight and left the airplane, never having completed the full inspection. The caps were left off.

It rained that entire weekend. The airplane sat out in the rain and nobody noticed that the caps were off and rainwater was entering the fuel tanks. On Sunday night the temperature dropped below the 32 degree freezing mark. On Monday morning another student and instructor checked out the airplane and began a preflight. When they arrived at the airplane, the fuel truck was just then pulling away. The lineman on duty that morning had stopped by the airplane to see if it needed fuel. He saw that the caps were off, but did not mention this to the pilots that were walking up. He simply saw that the tanks appeared to be full and drove away. The pilots thought that the lineman had just then filled the tanks and had left the caps off for their inspection.

The preflight inspection was cold, but routine — including the fuel check. Both the student and instructor looked at the fuel when it was sumped. It was clean, blue-tinted, aviation fuel, with no water. They thought that the caps had only been left off a few minutes since the fuel truck had just departed. They did not know that the caps had been off all weekend in the rain. Regardless, there was no visible water in the fuel sample. By the time the student pilot finished his inspection, strapped in, contacted the tower and made his way to the runway, the temperature had warmed to 40 degrees — a fine temperature for the student pilot as he embarked on his solo cross country.

The airplane flew, without incident … for 30 miles. Then, the engine sputtered, regained power, but then quit for good. The student pilot selected a field, flew what could have passed for a base and final leg, and landed unhurt. When the instructor, and several A&P technicians arrived at the scene, there was water in the fuel tanks and water contamination was determined to be the cause of the accident.

Did the rainwater that entered the tanks over the weekend freeze somewhere in the tanks on Sunday night? Did the frozen rainwater collect in the tanks somewhere other than the fuel drain, thus allowing a clean fuel sample to be drawn? Did the frozen rainwater eventually start to melt as the temperature rose and slowly contaminate the fuel? Was the time it took for the airplane to fly 30 miles the same time it took the ice to completely melt into the fuel system? Though important, all these questions are secondary.

…What about the caps being left off? The lineman, student pilots, and flight instructors all made assumptions — without ever talking to one another.

Always be aware of changing temperatures. Never walk or drive away from an airplane without securing the fuel caps — even on airplanes that you do not intend to fly — and, finally, if there is a question you don’t know the answer to … ask.