Definition 1 of 2
Definition
A method of joining two pieces of steel tubing in aircraft structure by cutting the end of one tube into a concave, V-shaped notch that matches the curved outer surface of the other tube, allowing the two ends to mate closely before being welded together.
Plain English
A way of joining two metal tubes by carving the end of one tube into a curved notch so it fits snugly around the side of the other tube, ready to be welded.
Context Anchor
Seen in aircraft maintenance and structural repair information for welded steel-tube airframes.
Derivation
Called a fishmouth splice because the cut end of the tube, with its two curved points and concave middle, looks like the open mouth of a fish. The shape itself tells you what the cut should look like.
Why Pilots Care
A properly made fishmouth splice keeps primary flight control cables strong and reliable, directly affecting control surface response and flight safety.
Analogy
It is like cutting the end of a straw into a curved notch so it fits neatly against another straw, instead of trying to join two flat ends that do not match well.
Intuition Check
Do not read “fishmouth” as a crack or damage by itself. In this term, it means the intentional curved shape cut into the repair piece.
Example Sentence 1
The mechanic cut a fishmouth splice into the end of the replacement tube so it would sit flush against the longeron before welding.
Example Sentence 2
Inspectors checked that the fishmouth splice on the rudder cable met the required pull-test strength.