Definition
The radial velocity of a moving target at which cancellation by a Moving Target Indicator (MTI) radar circuit causes the target to disappear from the display. When a target's speed toward or away from the radar antenna matches certain values tied to the radar's pulse rate, the MTI processing treats it as if it were stationary ground clutter and removes it from the screen.
Plain English
A specific speed at which an aircraft moving toward or away from a radar becomes invisible to that radar. The radar's filtering mistakes the aircraft for stationary ground and erases it from the controller's display.
Context Anchor
Seen in radar and air traffic control discussions, especially where radar tracking limits are being explained.
Derivation
Blind' here means the radar is unable to see the target -- not that the target is hidden physically, but that the radar's own processing has filtered it out. 'Velocity' specifies that it is the target's speed (specifically along the radar beam) that triggers this effect.
Why Pilots Care
Loss of radar contact can occur even when the aircraft is within normal range, affecting traffic advisories and separation services.
Intuition Check
“Blind” does not mean the pilot cannot see outside. Here it means the radar system may not see the aircraft correctly at a certain relative speed.
Example Sentence 1
The controller noted that the aircraft briefly disappeared from the scope, likely due to a blind velocity in the MTI radar.
Example Sentence 2
Controllers switched to secondary radar because several targets were showing blind velocity on the primary display.