Definition
A hole cut into a structural part — typically a rib, bulkhead, or web — to reduce its weight without significantly reducing its strength. The edges are usually flanged or rolled to maintain rigidity.
Plain English
A hole cut into a metal aircraft part to make it lighter. The shape and rolled edges keep the part strong while removing material that isn't needed.
Context Anchor
Seen in aircraft structure and maintenance discussions, especially when inspecting metal parts inside wings, fuselages, or control surfaces.
Derivation
From 'lighten' (to make less heavy) — not from 'lightning' the weather phenomenon. The spelling is a common point of confusion in maintenance documentation.
Why Pilots Care
On inspection, lightening holes are a normal design feature, not damage. Knowing this prevents misidentifying intentional holes as cracks, corrosion, or unauthorized modifications.
Intuition Check
Do not read this as “lightning hole,” and do not assume any hole in a part is a lightening hole. A lightening hole is intentional and is there to reduce weight while preserving enough strength.
Example Sentence 1
The wing rib had several lightening holes spaced along its length to reduce weight while keeping the structure rigid.
Example Sentence 2
Flanged lightening holes reduce weight while keeping the spar strong enough to handle flight loads.