Plain English Meaning
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.
Full 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.
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.