Plain English Meaning

Water getting into a composite part where it shouldn't be. Over time, especially when it freezes at altitude, that trapped water pushes the layers of the part apart and weakens it.

Full Definition

The unwanted entry and absorption of water into a composite aircraft structure, typically through small cracks, damaged paint, or unsealed edges. Once inside, the water can soak into the core material or sit between layers, where freezing temperatures at altitude expand the trapped water and progressively separate the bonded layers, weakening the structure.

Context Anchor

Seen in discussions of composite aircraft structures, inspections, and damage that may not be easy to see from the outside.

Derivation

From Latin 'ingressus,' meaning 'entry' or 'a going in.' So 'water ingress' literally means 'water going in' — water entering somewhere it isn't supposed to be.