B737 Undifferentiated or Other Model
Flight Crew Air Transport Pilot (ATP)
Communication Breakdown
ATC Issue All Types; Conflict Airborne Conflict
Flight Crew Took Evasive Action
Airspace Structure; Procedure
Level at 16;000 ft just north of ZZZZZ intersection we observed traffic on TCAS below and to the left of our position; climbing at a high rate. ATC never informed us of any traffic in our vicinity. Within seconds; we received a resolution advisory to descend. The Captain immediately started to comply with the TCAS resolution and started a descent until clear of conflict. I; as the Pilot Monitoring; tried to immediately notify ATC of the conflict; but I was unable to for about five to ten seconds due to radio congestion. As soon as possible; I notified Center that we were descending to comply with TCAS resolution. It seemed that ATC was not even aware of the traffic in our vicinity otherwise he may have given us at least an indication that there was another aircraft climbing towards us. Center then asked us what kind of resolution it was and at what altitude we had descended to; to which I replied a descent resolution and 15;000 ft. We were then handed to Approach and continued the visual approach without further incident.
Fifteen miles north of ZZZZZ on an enroute descent; we received an RA and responded correctly. We were level at 16;000 ft and descended to 15;000 ft feet as commanded. An aircraft below us was rapidly climbing into our altitude so we descended. Center was surprised at finding out we had descended due to an RA. It happened so fast that we never got a caution advisory; just an RA.
The flight crew of a 737 reported the need to comply with an RA to avoid an airborne conflict that ATC was seemingly unaware of.