Definition
A clear container, typically transparent plastic or glass, used during preflight to collect a small amount of fuel drained from the aircraft's fuel sumps so it can be visually inspected for water, sediment, and correct fuel grade by color.
Plain English
A see-through cup the pilot holds under the fuel drain to catch a little fuel and check that it is clean, water-free, and the right kind.
Context Anchor
Used during the preflight fuel check, especially when draining fuel from sumps or fuel drains before engine start.
Derivation
‘Sample’ comes from the Latin exemplum, meaning ‘a small part taken to represent the whole.’ The sample jar holds a small portion of fuel that represents the condition of all the fuel in the tank.
Why Pilots Care
Contaminated fuel can cause engine failure; the sample jar provides the only immediate visual confirmation that fuel is clean.
Intuition Check
Do not think of a sample jar as a storage jar or a way to measure total fuel onboard. In this context, it is a clear inspection container used briefly to check a small fuel sample.
Example Sentence 1
Before the first flight of the day, she drained fuel from each sump into the sample jar and held it up to the light to check for water.
Example Sentence 2
After inspecting the fuel, she emptied the sample jar and returned it to the side pocket of the cockpit door.