Definition
A surface failure in which small chips, flakes, or fragments break away from a hardened metal part, typically caused by repeated stress, fatigue, or subsurface cracking. Spalling is most often seen on the load-bearing surfaces of bearings, gears, and other hardened components.
Plain English
Tiny pieces flaking or chipping off the surface of a metal part, usually a bearing or gear, because of repeated heavy loading over time.
Context Anchor
Seen in aircraft maintenance reports and inspections, especially when checking metal parts such as bearings, gears, brake parts, and engine parts.
Derivation
From the Middle English 'spall,' meaning a chip or splinter of stone or metal. The word captures the idea exactly: small chips breaking off a hard surface.
Why Pilots Care
Spalling in bearings, gears, or propeller blades signals impending component failure that can cause loss of power or control.
Analogy
It is like the surface of old concrete or paint flaking off in small pieces. The main piece may still be there, but the surface is no longer healthy.
Intuition Check
Spalling does not mean a part is simply scratched or dirty. It means the surface material itself is breaking away.
Example Sentence 1
The mechanic cut open the oil filter during the inspection and found metal flakes consistent with bearing spalling.
Example Sentence 2
Continued flight with propeller spalling risks blade failure and loss of control.