Definition
A structural component installed crosswise between two main longitudinal members of an aircraft framework, used to tie those members together and resist twisting and bending loads. In a welded steel-tube fuselage, cross members run between the longerons; in a wing, they may run between spars.
Plain English
A piece of structure that runs sideways between two main lengthwise pieces, holding them together and keeping the frame rigid.
Context Anchor
Seen in airframe maintenance manuals, repair drawings, and inspection notes for fuselage, seat, landing gear, or engine-mount structures.
Derivation
Cross comes from the Latin crux, meaning a crosspiece. A cross member is literally a structural member that crosses between two others — the name describes exactly what it does.
Why Pilots Care
Cross members carry loads that keep the airframe square and true. Damage, corrosion, or improper repair to a cross member can compromise the strength of the entire structure, which is why structural inspections check them carefully.
Analogy
A cross member is like a rung between the two sides of a ladder: it ties the sides together and helps the whole structure stay rigid.
Intuition Check
Do not read cross member as just any part that crosses another part. In aircraft structure, it means a specific load-carrying piece that runs across and helps hold the structure together.
Example Sentence 1
The mechanic inspected the cross members between the longerons for cracks before signing off the annual.
Example Sentence 2
Reinforcing the wing cross members allowed the airplane to handle higher gust loads without deformation.