Definition
The external lever attached to the throttle or mixture shaft of an aircraft carburetor that the control cable connects to. When the pilot moves the throttle or mixture control in the cockpit, the cable rotates this arm, which in turn opens or closes the throttle butterfly valve or adjusts the fuel mixture inside the carburetor.
Plain English
A small metal lever sticking out of the carburetor. The cockpit throttle cable pulls or pushes this lever, which is how cockpit controls actually move parts inside the carburetor.
Context Anchor
You may hear this term during engine-system explanations, maintenance discussions, or a preflight check of the engine control linkages with the cowling open.
Derivation
Carburetor comes from the French 'carburer,' meaning to combine with carbon -- the device mixes fuel (carbon-based) with air. 'Arm' is used in its mechanical sense: a lever that transmits motion. So the carburetor arm is simply the lever on the carburetor that receives motion from the cockpit control.
Why Pilots Care
If the carburetor arm linkage is loose, bent, or improperly rigged, cockpit throttle or mixture inputs will not produce the expected engine response. Pilots check linkage security during preflight because a disconnected arm can cause loss of throttle control in flight.
Intuition Check
Do not think of arm as a human arm here. In this context, an arm is a small lever that transfers movement from a control cable to a mechanical part.
Example Sentence 1
During preflight, the pilot checked that the throttle cable was firmly attached to the carburetor arm and that the arm moved smoothly through its full range.
Example Sentence 2
During the run-up check, the instructor verified that the carburetor arm responded smoothly to throttle inputs.