Small transport pilot reported a TCAS warning on initial approach.

Attributes
ACN	1573497
Time
Date	201808
Local Time Of Day	0601-1200
Place
Locale Reference	ZZZ.Airport
State Reference	US
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Make Model Name	Small Transport Low Wing 2 Turbojet Eng
Operating Under FAR Part	Part 91
Flight Phase	Initial Approach
Route In Use	Visual Approach
Flight Plan	IFR
Person 1
Function	Pilot Not Flying
Qualification	Flight Crew Multiengine Flight Crew Instrument Flight Crew Air Transport Pilot (ATP)
Experience	Flight Crew Last 90 Days 125 Flight Crew Total 9400 Flight Crew Type 1300
Events
Anomaly	ATC Issue All Types Conflict NMAC Deviation - Procedural Clearance
Miss Distance	Horizontal 100 Vertical 500

Narrative:

While within the class B airspace; 10 miles north of ZZZ; we called the airport 'in sight' and were cleared for a visual approach to ZZZ runway xx. As we began our descent from 4;000 MSL; we noticed a target on TCAS 500 ft below our altitude approaching our path from the east. We stopped our descent while looking for the traffic. Then the [TCAS] commanded a climb as the aircraft neared our location. We began a climb as the aircraft passed below us. When TCAS stated clear of conflict; we continued our approach to ZZZ. I reported our conflict to ZZZ tower; and we were cleared to land on xx. VFR traffic below the class B airspace combined with our clearance for a visual approach contributed to our conflict within 500 ft vertical. We never saw the other aircraft. [TRACON] was busy; but a warning that the aircraft was below us and converging on our track to the airport could have delayed our descent; and avoided the conflict.

Original NASA ASRS Text

Title: Small Transport pilot reported a TCAS warning on initial approach.

Narrative: While within the class B airspace; 10 miles North of ZZZ; we called the airport 'in sight' and were cleared for a visual approach to ZZZ runway XX. As we began our descent from 4;000 MSL; we noticed a target on TCAS 500 ft below our altitude approaching our path from the East. We stopped our descent while looking for the traffic. Then the [TCAS] commanded a climb as the aircraft neared our location. We began a climb as the aircraft passed below us. When TCAS stated clear of conflict; we continued our approach to ZZZ. I reported our conflict to ZZZ tower; and we were cleared to land on XX. VFR traffic below the Class B airspace combined with our clearance for a visual approach contributed to our conflict within 500 ft vertical. We never saw the other aircraft. [TRACON] was busy; but a warning that the aircraft was below us and converging on our track to the airport could have delayed our descent; and avoided the conflict.

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.