Definition
A flexible, airtight rubber tube fitted inside a tube-type aircraft tire that holds the pressurized air. The tube has a valve stem that passes through a hole in the wheel, allowing the tube to be inflated and deflated. In tube-type wheels, the tube — not the tire itself — is what actually contains the air pressure.
Plain English
A rubber bladder shaped like a doughnut that sits inside the tire and holds the air. You pump the tire up by inflating the tube inside it.
Context Anchor
Seen in aircraft tire maintenance, wheel servicing, and inspections of tube-type tires.
Why Pilots Care
A leaking or damaged inner tube can cause sudden loss of tire pressure, affecting ground handling and braking.
Analogy
Think of an old bicycle tire: the rubber tube inside is what actually holds the air, while the outer tire protects the tube and grips the ground. Aircraft inner tubes work the same way.
Intuition Check
Do not think of the inner tube as the whole tire. The inner tube is only the air container inside a tube-type tire.
Example Sentence 1
After finding the tire low again, the mechanic pulled the wheel apart and discovered a small puncture in the inner tube.
Example Sentence 2
Many modern aircraft use tubeless tires and no longer require an inner tube.