Definition
The radial velocity of a moving target such that the target is not seen on primary radars fitted with certain forms of fixed echo suppression.
Plain English
A speed at which an aircraft moving toward or away from a radar becomes invisible to that radar. The radar has a built-in filter that removes signals from things sitting still on the ground, and an aircraft moving at just the right speed gets removed by that same filter by accident.
Context Anchor
Seen in radar surveillance and air traffic control discussions, especially when describing limits of certain radar systems.
Derivation
‘Blind’ here means the radar cannot see the target, not that the target itself is blind. ‘Velocity’ is used in its precise sense — speed in a specific direction (toward or away from the radar) — not just speed in general. The phrase describes the specific speed at which the radar goes blind to the aircraft.
Why Pilots Care
May cause temporary loss of primary radar contact, requiring reliance on secondary surveillance radar or procedural separation.
Intuition Check
Blind velocity does not mean the pilot is blind or the aircraft has no visibility. It means a radar may not show a target at a certain speed toward or away from the radar antenna.
Example Sentence 1
The controller noted that the target faded briefly, possibly due to a blind velocity condition on the primary radar.
Example Sentence 2
Controllers plan separation assuming possible blind velocity gaps when only primary radar is available.