Dhc-8 flight crew reported a TCAS RA for unreported traffic while on approach.

Attributes
ACN	1505787
Time
Date	201712
Local Time Of Day	1201-1800
Place
Locale Reference	ZZZ.Airport
State Reference	US
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Make Model Name	Dash 8-300
Operating Under FAR Part	Part 121
Flight Phase	Initial Approach
Flight Plan	IFR
Person 1
Function	Captain Pilot Not Flying
Qualification	Flight Crew Air Transport Pilot (ATP)
Person 2
Function	First Officer Pilot Flying
Qualification	Flight Crew Air Transport Pilot (ATP)
Experience	Flight Crew Last 90 Days 120 Flight Crew Total 7000 Flight Crew Type 700
Events
Anomaly	Conflict Airborne Conflict

Narrative:

While being vectored for approach; we received a TCAS RA directing us to climb after having received a TCAS TA. We immediately climbed by approximately 700 ft until the TCAS system stopped giving us a climb command. We notified approach of the TCAS RA and that we were in a climb. Once the command ended; we returned to our previously assigned altitude and advised approach. We didn't see the TCAS intruder until we began our climb; it appeared to be a single engine aircraft at a VFR altitude of approximately 4;500 ft. We had been assigned a vectoring altitude of 5;000 ft. After we returned to our previously assigned altitude; the rest of the flight was uneventful.

Original NASA ASRS Text

Title: DHC-8 flight crew reported a TCAS RA for unreported traffic while on approach.

Narrative: While being vectored for approach; we received a TCAS RA directing us to climb after having received a TCAS TA. We immediately climbed by approximately 700 ft until the TCAS system stopped giving us a climb command. We notified approach of the TCAS RA and that we were in a climb. Once the command ended; we returned to our previously assigned altitude and advised Approach. We didn't see the TCAS intruder until we began our climb; it appeared to be a single engine aircraft at a VFR altitude of approximately 4;500 ft. We had been assigned a vectoring altitude of 5;000 ft. After we returned to our previously assigned altitude; the rest of the flight was uneventful.

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.