Definition
The complete unit at the rear of a tailwheel-type airplane consisting of a small wheel mounted under the tail, its supporting structure, and the steering or castering mechanism that connects it to the rudder pedals. On most designs, the tailwheel can be steered through the rudder pedals up to a certain deflection, beyond which it unlocks and swivels freely to allow tighter turns.
Plain English
The small wheel and its supporting parts at the back of an airplane that has its third wheel under the tail instead of under the nose. The pilot usually steers it with the rudder pedals during taxi.
Context Anchor
You will see this term when learning how tailwheel airplanes taxi, turn, and stay under control on the ground.
Why Pilots Care
Correct use prevents ground loops and loss of directional control, especially in crosswinds, because tailwheel airplanes have limited steering authority at the rear.
Intuition Check
Do not read this as just the tire or wheel. In aviation use, tailwheel assembly means the whole rear wheel unit, including the parts that hold it and help it work.
Example Sentence 1
During the preflight, the pilot checked the tailwheel assembly for cracks in the spring and made sure the steering chains were properly tensioned.
Example Sentence 2
In a strong crosswind the pilot applies full rudder and differential braking because the tailwheel assembly offers only limited steering response at low speeds.