Definition
The plane in which a spinning gyroscope actually responds when a force is applied to it. Because of the gyroscope's rigidity, an applied force does not produce movement at the point of application. Instead, the response appears 90 degrees ahead of that point in the direction of rotor spin. That resulting plane of motion is the plane of precession.
Plain English
When you push on a spinning gyro, it doesn't tip the way you'd expect. It tips in a different direction — 90 degrees around from where you pushed, measured in the direction the gyro is spinning. The plane of precession is simply the plane in which that surprising tipping motion takes place.
Context Anchor
Seen in discussions of turn indicators, where a spinning gyro is mounted so its precession can be used to show aircraft turning.
Derivation
Precession comes from the Latin praecedere, meaning 'to go before' or 'come ahead.' That fits exactly here: the gyro's reaction shows up ahead of where the force was applied, measured around the spinning rotor.
Why Pilots Care
It explains the 90-degree offset that lets turn indicators accurately display rate of turn through gyroscopic reaction.
Analogy
A spinning bicycle wheel can react in a surprising direction when you try to tilt it. The plane of precession is the flat path where that reaction movement takes place.
Grounding Statement
Push down on the front of a spinning bicycle wheel held by its axle, and instead of tipping forward, it twists sideways. The sideways twist is happening in the plane of precession.
Intuition Check
Plane does not mean an airplane here; it means an imaginary flat surface or path. Precession does not mean ordinary turning; it means the special way a spinning gyro reacts to a force.
Example Sentence 1
The turn indicator works by letting the gyro tilt freely in its plane of precession when the aircraft yaws.
Example Sentence 2
The plane of precession determines the direction the turn coordinator needle deflects during a coordinated turn.