Definition
A small manual or electric pump in the aircraft's fuel system that injects raw fuel directly into the intake ports or cylinders of the engine to aid starting, particularly in cold conditions.
Plain English
A pump the pilot uses to squirt a little fuel into the engine before starting it, so the engine has something to burn when it first turns over.
Context Anchor
Seen during engine-start procedures, including hand propping, when the pilot prepares the engine before the propeller is turned.
Derivation
From the verb 'prime,' meaning to prepare something for action by filling or charging it. Same idea as priming a water pump — adding a small amount first so the system can start working on its own.
Why Pilots Care
A properly used primer ensures reliable starts in cold weather or after long periods of inactivity, reducing the risk of a prop strike or incomplete start during hand propping.
Analogy
Like priming an old-fashioned water pump by pouring a cup of water into it so the pump can begin drawing from the well on its own.
Intuition Check
Primer does not mean paint or a beginner lesson here. In this context, it means the control that prepares the engine to start by adding a small amount of fuel.
Example Sentence 1
On a cold morning, the pilot gave the engine two strokes of the primer before turning the key.
Example Sentence 2
On a cold morning the primer was used again after the first start attempt failed to catch.