Definition
The permissible amount of variation from a specified dimension, value, or standard. In maintenance, tolerance defines the upper and lower limits within which a measured part, clearance, torque value, or operating parameter is still considered acceptable.
Plain English
How much a measurement is allowed to differ from the exact target value before the part or setting is no longer acceptable.
Context Anchor
Seen in aircraft maintenance manuals, inspection procedures, parts drawings, and adjustment instructions where a measured value must fall within an allowed range.
Derivation
From the Latin tolerare, meaning 'to bear' or 'to endure.' In engineering, it refers to how much variation a design can 'bear' before performance or safety is affected.
Why Pilots Care
Parts that stay inside tolerance fit and operate correctly; parts outside tolerance can cause vibration, leaks, or structural failure.
Analogy
If a recipe says an oven should be 350°F, a small difference may be acceptable, but a large difference may ruin the result. Tolerance is that allowed difference.
Intuition Check
Tolerance does not mean patience or willingness to put up with something here. In aviation maintenance, it means the permitted amount of variation from a required value.
Example Sentence 1
The mechanic measured the cylinder bore and found it was within the tolerance specified in the overhaul manual.
Example Sentence 2
The fuel line pressure must stay within tolerance during the engine run-up test.