Definition
The preflight procedure of draining a small quantity of fuel from each fuel tank sump and from the fuel strainer (gascolator) into a clear sampler cup, then visually inspecting it for water, sediment, and the correct fuel grade and color before flight.
Plain English
Pulling a small sample of fuel from the low points of the fuel system into a clear cup so you can check that there is no water or dirt in the fuel and that it is the right type.
Context Anchor
You do this during the preflight inspection, usually with a fuel sample cup or tester at each fuel drain point listed for the airplane.
Derivation
A 'sump' is the lowest point of a tank or container, where heavier contaminants like water and dirt naturally settle. 'Sumping' means drawing fluid from that low point. The word comes from Middle English and Dutch terms meaning a marsh or pool — a low spot where liquid collects.
Why Pilots Care
Water or debris in the fuel can cause engine stoppage; sumping removes the risk before takeoff.
Grounding Statement
Because water is heavier than aviation gasoline, it can settle below the fuel where a sump drain can reveal it.
Intuition Check
Sumping the fuel system does not mean draining all the fuel from the airplane. It means draining a small sample from specific low points to check fuel quality.
Example Sentence 1
After fueling the airplane, the pilot spent a few extra minutes sumping the fuel system because the aircraft had been parked overnight in heavy rain.
Example Sentence 2
After fueling from a truck the pilot sumped the fuel system again to confirm the fuel remained clean.