Pao tower controller reported a near midair collision between an aircraft in their pattern and an ai...

Narrative:

I was working local and controller in charge position. I got a call on the shout line from nuq tower asking me if I had their traffic in sight; aircraft X. I looked out the window because it had a low altitude alert and saw the aircraft when they were around pudby intersection and I told them I had them in sight. Aircraft X was landing/dep. 14 at nuq and we were landing/dep. 13 and we are 5 miles apart. At the time I had an aircraft Z and aircraft Y in traffic pattern; the aircraft Z was doing a touch and go; and soon after I cleared the aircraft Y I kept aircraft X insight outside the window but did not correlate the altitude with the radar. I noticed the aircraft X has not started their turn to base; while my aircraft Y was on the departure end so I told the aircraft Y to start his crosswind turn and stop his climb. Once the aircraft X started his base turn 1/2 mile in my upwind; nuq did say he had my aircraft Y insight. Aircraft X had aircraft Y in sight but I did not give traffic to the aircraft Y; which I believe played a crucial part in this. The aircraft X overflew the aircraft Y when they were turning downwind. The aircraft Y was at 600 ft and aircraft X 800 ft. I recommend that aircraft that are circling west of nuq landing 14 during VFR conditions should cross pao field above 1300 for local pao traffic.

Original NASA ASRS Text

Title: PAO Tower Controller reported a NMAC between an aircraft in their pattern and an aircraft deviating from the adjacent airports final approach course.

Narrative: I was working Local and CIC position. I got a call on the shout line from NUQ Tower asking me if I had their traffic in sight; Aircraft X. I looked out the window because it had a Low Altitude alert and saw the aircraft when they were around PUDBY intersection and I told them I had them in sight. Aircraft X was landing/dep. 14 at NUQ and we were landing/dep. 13 and we are 5 miles apart. At the time I had an Aircraft Z and Aircraft Y in traffic pattern; the Aircraft Z was doing a touch and go; and soon after I cleared the Aircraft Y I kept Aircraft X insight outside the window but did not correlate the altitude with the radar. I noticed the Aircraft X has not started their turn to base; while my Aircraft Y was on the departure end so I told the Aircraft Y to start his crosswind turn and stop his climb. Once the Aircraft X started his base turn 1/2 mile in my upwind; NUQ did say he had my Aircraft Y insight. Aircraft X had Aircraft Y in sight but I did not give traffic to the Aircraft Y; which I believe played a crucial part in this. The Aircraft X overflew the Aircraft Y when they were turning downwind. The Aircraft Y was at 600 ft and Aircraft X 800 ft. I recommend that aircraft that are circling west of NUQ landing 14 during VFR conditions should cross PAO field above 1300 for local PAO traffic.

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.

Attributes
ACN	1645809
Time
Date	201905
Local Time Of Day	1801-2400
Place
Locale Reference	PAO.Tower
State Reference	CA
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Make Model Name	Medium Transport Low Wing 2 Turbojet Eng
Operating Under FAR Part	Part 91
Flight Phase	Final Approach
Route In Use	Visual Approach
Flight Plan	IFR
Aircraft 2
Make Model Name	Small Aircraft Low Wing 1 Eng Fixed Gear
Operating Under FAR Part	Part 91
Flight Phase	Other VFR Traffic Pattern
Route In Use	Other VFR Pattern
Flight Plan	VFR
Person 1
Function	Local Supervisor / CIC
Qualification	Air Traffic Control Fully Certified
Experience	Air Traffic Control Time Certified In Pos 1 (yrs) 1
Events
Anomaly	ATC Issue All Types Conflict NMAC

Pao tower controller reported a near midair collision between an aircraft in their pattern and an aircraft deviating from the adjacent airports final approach course.