Definition
A transparent, rounded protrusion on the exterior of an aircraft fuselage that houses equipment such as an observation station, gun position, antenna, or sensor. The blister extends beyond the normal skin line of the aircraft to provide an unobstructed field of view or signal coverage.
Plain English
A bubble-shaped bulge on the outside of an aircraft, usually clear, that sticks out from the body to give a crew member or piece of equipment a wider view or better reach in all directions.
Context Anchor
Seen during aircraft inspections of paint, composite parts, fabric covering, sealant, or other bonded surfaces.
Derivation
From the everyday word 'blister' — a small raised bubble on a surface, like a blister on skin. The aviation use borrows the visual idea: a rounded bump rising from an otherwise smooth surface.
Why Pilots Care
Gives crew members a wider field of view or firing arc without major drag penalty.
Analogy
It is like a bubble under a phone screen protector or under old paint on a wall. The top layer may still be there, but it is no longer firmly attached underneath.
Intuition Check
A blister is not just a cosmetic bump. In aircraft use, it can mean a layer has separated and may need inspection before the part is considered sound.
Example Sentence 1
The gunner's blister on the side of the bomber gave a clear view in every direction.
Example Sentence 2
During preflight the pilot checked the blister for cracks or loose fasteners.