Definition
A condition of the nosewheel (or tailwheel) in which it is unlocked from the rudder pedal steering linkage and free to rotate, or 'castor,' through a wide arc -- often a full 360 degrees -- in response to differential braking and thrust rather than direct pilot steering input.
Plain English
The nosewheel is set free to spin in any direction on its own. Instead of steering it with the rudder pedals, the pilot turns the airplane by braking one main wheel harder than the other.
Context Anchor
Encountered while taxiing tailwheel airplanes, especially during tight turns on ramps, near parking areas, or in confined spaces.
Derivation
Swivel' comes from an Old English root meaning to turn or rotate freely, related to the verb 'to wind.' 'Full swivel' simply means the wheel can rotate fully -- not limited to a small steering arc.
Why Pilots Care
It permits tight-radius maneuvering without heavy brake use or risk of stressing the gear, reducing the chance of ground loops in tailwheel airplanes.
Intuition Check
Full swivel mode does not mean maximum normal steering. It means the tailwheel is unlocked and can rotate freely, so the airplane can pivot much more sharply than usual.
Example Sentence 1
Because the trainer's nosewheel is in full swivel mode, the instructor demonstrated how to use light braking on the inside main wheel to start the turn.
Example Sentence 2
With the nose gear in full swivel mode, differential power and light braking allowed the airplane to pivot within one wingspan.