Pilot reported a near midair collision while on base leg.

Attributes
ACN	1757708
Time
Date	202008
Local Time Of Day	1801-2400
Place
Locale Reference	ZZZ.Tower
State Reference	US
Environment
Flight Conditions	VMC
Light	Night
Aircraft 1
Make Model Name	A319
Operating Under FAR Part	Part 91
Flight Phase	Final Approach
Route In Use	Vectors
Flight Plan	IFR
Aircraft 2
Make Model Name	Any Unknown or Unlisted Aircraft Manufacturer
Person 1
Function	Captain Pilot Flying
Qualification	Flight Crew Multiengine Flight Crew Air Transport Pilot (ATP) Flight Crew Instrument
Experience	Flight Crew Last 90 Days 190 Flight Crew Total 5400
Events
Anomaly	Conflict NMAC Deviation - Altitude Excursion From Assigned Altitude Deviation - Procedural Published Material / Policy Deviation - Procedural Clearance
Miss Distance	Horizontal 3 Vertical 500

Narrative:

Monitor vertical speed on TCAS on base leg prior to turn on final. Traffic was at 500 ft below our altitude at all times and procedure was done accordingly to SOP's. A go around was performed after leveling off at 2;500 ft since continue to land with an stabilized approach was not possible.

Original NASA ASRS Text

Title: Pilot reported a NMAC while on base leg.

Narrative: Monitor Vertical Speed on TCAS on base leg prior to turn on final. Traffic was at 500 ft below our altitude at all times and procedure was done accordingly to SOP's. A go around was performed after leveling off at 2;500 ft since continue to land with an stabilized approach was not possible.

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.