Definition
The radial speed of a target, relative to a radar antenna, at which the radar's moving target indicator (MTI) cannot distinguish the target from stationary ground returns, causing the target to disappear from the controller's display.
Plain English
A specific speed at which an aircraft, moving directly toward or away from a radar site, briefly becomes invisible to that radar because its motion looks like ground clutter to the radar's filter.
Context Anchor
Seen in radar and air traffic control discussions, especially when explaining why a primary radar target may be weak or temporarily lost.
Derivation
Called 'blind' because the radar is effectively blind to the aircraft at that speed — not because anything is wrong with the aircraft or the controller, but because the radar's filter for stationary objects accidentally filters out the aircraft too.
Why Pilots Care
A pilot flying at or near a blind speed may disappear from controller radar displays without warning, requiring extra position reports or altitude changes to restore contact.
Grounding Statement
An aircraft can be moving normally, but if its motion toward or away from the radar falls into a speed the radar filter cancels, the target may fade from the display.
Intuition Check
Blind speed does not mean flying without outside vision or flying in clouds. Here, blind means the radar may fail to see the aircraft clearly at a particular speed relative to the radar antenna.
Example Sentence 1
The controller advised that the aircraft had momentarily faded from the scope, likely due to a blind speed condition along that radial.
Example Sentence 2
Because the jet was climbing through a blind speed region, primary radar returns were lost until the pilot leveled off.