Definition
A painted line drawn across the joint between a tire and its wheel rim, used to detect whether the tire has rotated (slipped) on the rim. If the two halves of the line no longer align, the tire has shifted on the wheel, which can shear the valve stem and cause sudden deflation.
Plain English
A line of paint that runs from the tire onto the wheel. If the line still lines up, the tire hasn't moved on the wheel. If it's offset, the tire has slipped and needs attention.
Context Anchor
Seen during aircraft tire and wheel inspections, especially after tire installation, hard braking, or a suspected tire problem.
Derivation
From 'slippage' (the act of slipping) plus 'mark' (a visible indicator). The name describes exactly what the mark is for: showing whether slipping has occurred.
Why Pilots Care
Detects tire slippage that can cause imbalance, vibration, or sudden tire failure.
Intuition Check
Do not read “slippage mark” as a random scuff or damage mark. It is a deliberate reference line used to detect unwanted tire movement on the wheel.
Example Sentence 1
During preflight, the technician noticed the slippage mark on the main gear tire was misaligned by about an inch, indicating the tire had rotated on the rim.
Example Sentence 2
After landing the mechanic noticed the slippage mark had shifted, so the tire was removed for inspection.