Flight Crew Instrument; Flight Crew Multiengine; Flight Crew Air Transport Pilot (ATP)
Time Pressure; Workload; Confusion; Situational Awareness
ATC Issue All Types; Conflict NMAC
Flight Crew FLC complied w / Automation / Advisory; Flight Crew Requested ATC Assistance / Clarification; Flight Crew Took Evasive Action; Flight Crew Returned To Clearance
Airspace Structure; Human Factors
We were held down at 5;000 feet for traffic while essentially on a left downwind departure. After flying level at 5;000 feet for a couple of minutes we were cleared to climb to 16;000 feet. Once established in the climb and climbing out of 6;000 feet; we were climbing at a rather high rate. As we were established in climb; we received a TCAS TA on traffic at 1 o'clock; which appeared to be converging on us. No sooner than we noticed; we received a 'DESCEND; DESCEND' TCAS RA. I disconnected the autopilot and autothrottles while simultaneously idling the thrust levers and pitching down to comply with the RA. Essentially; we went from full climb thrust in a climb at 250 knots below 10;000 feet to needing to descend promptly. That's a pretty dramatic change of aircraft energy state. I saw from the corner of my eye that it appeared to be a twin turboprop. The conflict aircraft passed right over us; most certainly less than 500 feet.  As we were descending in our RA maneuver; ATC warned us to stop climb immediately. We informed him we were responding to TCAS RA already. After the threat aircraft was behind us; we resumed our climb and queried ATC as to why they didn't point out the traffic to us. The Controller said he 'didn't see him and wasn't talking to him.' I found that answer to be strange; but as it turned out; the top of the Class B airspace was below us. We reported the event to Dispatch and the Captain filed an incident report as per the policy. The question I have is whether the ATC can somehow remove VFR targets outside of their airspace band that are squawking VFR and wonder if that's what happened here. The threat aircraft was well within his rights to fly VFR above Class B airspace without talking to ATC; but without TCAS and without Controller pointing out traffic; because they may be 'squelching' VFR traffic outside of Class B; this could have ended really badly especially considering several cloud layers that we encountered. I recently flew an aircraft with TCAS MELed and I'm sure glad this happened when we actually had a functioning TCAS.
Air carrier pilot climbing on departure reported a NMAC with an unidentified VFR aircraft just above the Class B Airspace ceiling. ATC stated they 'did not see' the aircraft so did not issue traffic to the air carrier.