Date: 201511
Local time of day: 1201-1800
Location: SNA.Airport, CA
Light: Daylight
Aircraft: B737 Undifferentiated or Other Model
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Takeoff / Launch
Airspace: Class C SNA
ATC / advisory: Tower SNA
Second aircraft: Gulfstream Jet Undifferentiated or Other Model
Reporter organization: Government
Reporter function: Local
Reporter qualification: Air Traffic Control Fully Certified
Human factors: Situational Awareness; Human-Machine Interface; Confusion; Distraction
Anomaly: ATC Issue All Types; Conflict Airborne Conflict; Deviation / Discrepancy - Procedural Published Material / Policy
Detector: Person Air Traffic Control
When detected: In-flight
Result: Air Traffic Control Provided Assistance
Contributing factors: ATC Equipment / Nav Facility / Buildings; Airspace Structure; Procedure
Primary problem: ATC Equipment / Nav Facility / Buildings

Narrative: I was working Local Control. We were on north traffic; which I have not worked since last year and I was taking things slow. I launched a small twin IFR aircraft and he was to fly a 340 degree heading on departure. However; with the strong winds; the aircraft seemed to be drifting east (remaining on the final) instead of turning left to a 340 heading. I had Aircraft X in position and Aircraft Y on final. I launched Aircraft X and told him to depart without delay and then cleared Aircraft Y to land. I thought there would be plenty of room; but as Aircraft X was rolling it seemed like Aircraft Y moved quicker on the radar than I expected and when Aircraft X was towards the departure end of the runway; Aircraft Y was crossing landing threshold.Our people have noticed that over the last month since we have gotten our Fusion and Standard Terminal Automation Replacement System (STARS) that the radar targets start to drift and move in funny directions as the aircraft are on the final and departing. I am not sure if that played a factor in this event by misrepresenting Aircraft Y on final or if that had anything to do with him seeming to move quicker on the final; but I have not had a misjudgment like this before. Our radar was out of service the prior day and the techs need to take it out again in the near future for some more maintenance. I am not sure what they are fixing. I am not trying to deflect the events; I just wanted to make it know.Like I said; I have not worked north traffic in a while. However; with the implementation of Fusion and STARS; I will be increasing my cut off points to account for any inaccuracies that may occur with the radar. This is not something I thought I would ever have to type; and I am not happy. For recommendations; I should have taken Aircraft X off the runway; or sent Aircraft Y around looking back at the event.




Synopsis: A Tower Controller cleared an aircraft for takeoff with another on short final. The Controller may not have had enough spacing between the arrival and departure. The Controller is not sure because the arrival radar target was rapidly drifting and changing positions on the radar display. This facility has recently acquired Standard Terminal Automation Replacement System (STARS) radar displays and FUSION software. Since transitioning to this new equipment the reporter has notice the radar target inaccuracies close in to the airport.