Definition
The procedure of adjusting a turbine engine's fuel control unit so the engine produces its rated thrust at a specified set of operating conditions. Trimming is performed on the ground using a calibrated test set, with the engine running, and is done after fuel control replacement, certain maintenance actions, or when performance checks show the engine is not meeting its target output.
Plain English
Fine-tuning a jet engine on the ground so it produces exactly the power it is supposed to produce.
Context Anchor
Seen in aircraft maintenance procedures, especially after engine work, fuel control replacement, or a required engine run-up check.
Derivation
From the nautical sense of 'trim' -- making small adjustments so a vessel runs correctly. Carried into engineering to mean fine adjustment of a system to bring it to its intended performance.
Why Pilots Care
Correct trimming prevents engine damage, ensures reliable power output, and maintains fuel efficiency and safety margins.
Intuition Check
Do not read trimming here as cutting something off. In this context, trimming means adjusting the engine controls until the engine runs within the required limits.
Example Sentence 1
After replacing the fuel control unit, the mechanic performed an engine trimming check to confirm the engine produced its rated thrust.
Example Sentence 2
The pilot confirmed engine trimming was complete before the first flight of the day.