Definition
On an ARTS III or DBRITE radar display, a controlled partial data block is the alphanumeric tag attached to a radar target representing an aircraft that is receiving air traffic control services but for which the full data block (showing identification, altitude, and groundspeed) is not currently displayed. It typically shows limited information, such as a Mode C altitude readout, indicating the aircraft is being worked by a controller but the complete tag has been suppressed or not yet associated.
Plain English
It is the short label next to a radar blip on the controller's screen for an aircraft the controller is handling, showing only some of the aircraft's information instead of all of it.
Context Anchor
Seen on terminal radar displays, including the ARTS III / DBRITE display shown in the Instrument Flying Handbook.
Derivation
Controlled means the aircraft is being actively worked by a controller. Partial means only some of the information appears. Data block is the cluster of letters and numbers shown next to the radar return. Together: a shortened tag for an aircraft that is under ATC control.
Why Pilots Care
Pilots rarely see these displays directly, but understanding what controllers see helps explain why ATC may ask for verification of altitude or identification, and why clear, prompt readbacks matter when the controller's screen shows limited information about your aircraft.
Intuition Check
Controlled does not mean the controller is flying the aircraft. Partial does not mean uncertain or incomplete in a careless way; it means the display is intentionally showing a reduced amount of information.
Example Sentence 1
On the DBRITE display, the VFR aircraft transitioning the Class C airspace appeared as a controlled partial data block showing only its Mode C altitude.
Example Sentence 2
As the flight entered controlled airspace, the radar changed its tag to a controlled partial data block.