Ffz tower controller reported overlooking a potential conflict between an arriving and departing air...

Attributes
ACN	1487442
Time
Date	201710
Local Time Of Day	1801-2400
Place
Locale Reference	FFZ.Tower
State Reference	AZ
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Make Model Name	PA-28R Cherokee Arrow All Series
Operating Under FAR Part	Part 91
Flight Phase	Initial Approach
Route In Use	Visual Approach
Flight Plan	IFR
Aircraft 2
Make Model Name	PA-28 Cherokee/Archer/Dakota/Pillan/Warrior
Operating Under FAR Part	Part 91
Flight Phase	Climb
Route In Use	Vectors
Flight Plan	VFR
Person 1
Function	Local
Qualification	Air Traffic Control Fully Certified
Experience	Air Traffic Control Time Certified In Pos 1 (yrs) 8.0
Events
Anomaly	ATC Issue All Types Conflict NMAC
Miss Distance	Horizontal 0 Vertical 400

Narrative:

Aircraft X checked in 8 south and was instructed to make left traffic runway 22L. Aircraft Y was departure roll for a south bound departure. As aircraft Y started his southbound turn I recognized his course converging with aircraft X. I issued traffic when they were over a mile apart. Aircraft X reported aircraft Y in sight below him when they were about 3/4 of a mile apart. It appeared that aircraft X passed approximately 400 ft above aircraft Y. I found out today that aircraft Y reported a near midair collision regarding this incident.I should have recognized the conflict sooner and issued instructions like have aircraft Y fly straight out till he was passed aircraft X.

Original NASA ASRS Text

Title: FFZ Tower Controller reported overlooking a potential conflict between an arriving and departing aircraft until they were almost converging.

Narrative: Aircraft X checked in 8 south and was instructed to make left traffic RWY 22L. Aircraft Y was departure roll for a south bound departure. As Aircraft Y started his southbound turn I recognized his course converging with Aircraft X. I issued traffic when they were over a mile apart. Aircraft X reported Aircraft Y in sight below him when they were about 3/4 of a mile apart. It appeared that Aircraft X passed approximately 400 ft above Aircraft Y. I found out today that Aircraft Y reported a NMAC regarding this incident.I should have recognized the conflict sooner and issued instructions like have Aircraft Y fly straight out till he was passed Aircraft X.

Data retrieved from NASA's ASRS site and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.

Ffz tower controller reported overlooking a potential conflict between an arriving and departing aircraft until they were almost converging.