B737 Next Generation Undifferentiated
Flight Crew Air Transport Pilot (ATP)
Flight Crew Last 90 Days 175; Flight Crew Type 9110
Communication Breakdown
ATC Issue All Types; Conflict NMAC; Deviation / Discrepancy - Procedural Published Material / Policy
Flight Crew Took Evasive Action; Flight Crew FLC complied w / Automation / Advisory
Airspace Structure; Environment - Non Weather Related
The First Officer (FO) took off from ZZZ on runway heading Runway 6. After a direct clearance and another vector off the SID for traffic; we were cleared direct to ZZZ VOR with a climb to FL230. Direct ZZZ VOR was executed with abeam points; and we initiated the climb. Just prior to the ZZZZZ Intersection; abeam point and approximately FL200; we received an aural 'TRAFFIC' advisory. The FO slowed his rate of climb to 800 FPM using Vertical Speed (VS) to avoid setting off an RA since the other aircraft was above us. I noticed the aircraft was only 400 feet above us on the HSI and barely acquired the traffic visually when the TCAS commanded a 'CLIMB' RA. The FO immediately disconnected the autopilot; pushed the thrust levers up and initiated a climb maneuver following the RA command on the flight director. After a brief moment of climbing at an increased VS; the TCAS issued a 'CLEAR OF CONFLICT' advisory. Start to finish; the whole incident happened very quickly. I re-acquired the traffic passing to our left from beneath our nose at our 11 o'clock position and low. The Controller started to give us a Traffic Advisory but didn't really finish because the aircraft had already passed. I told the Controller that it had set off an RA in our aircraft. In the end; we had climbed through the other aircraft's altitude as a result of following the TCAS RA; and I believe we passed within three NM of the other aircraft. Being at night; it was more difficult to tell. There were several quick frequency changes that might have contributed on the Controllers' part. We notified Dispatch through ACARS. We continued the flight without further incident.Understand what conditions led to the RA and correct it/them. It was either a Controller error/misjudgment or a Pilot error in either/both aircraft. Additionally; it was a clearance not being given or received properly. I believe that we complied fully with ATC clearances and our TCAS/RA maneuver.
A B737 Captain reported  a 'CLIMB' RA despite the traffic above.