Date: 201308
Local time of day: 1801-2400
Location: BOS.Airport, MA
Flight conditions: VMC
Light: Night
Aircraft: B737-800
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Flight phase: Initial Approach
Airspace: Class B BOS
ATC / advisory: TRACON A90
Second aircraft: Any Unknown or Unlisted Aircraft Manufacturer
Reporter organization: Air Carrier
Reporter function: First Officer; Pilot Not Flying
Human factors: Physiological - Other; Situational Awareness; Communication Breakdown
Second reporter function: Captain; Pilot Flying
Anomaly: ATC Issue All Types; Conflict Airborne Conflict; Conflict NMAC
Detector: Automation Aircraft RA; Automation Aircraft TA
When detected: In-flight
Result: Flight Crew Took Evasive Action; Flight Crew FLC complied w / Automation / Advisory
Contributing factors: Environment - Non Weather Related; Procedure; Human Factors
Primary problem: Ambiguous

Narrative: Last night on approach into Boston we received an RA during which the Captain had to maneuver the airplane to avoid an imminent collision. We were on vectors to 27 and on downwind. We were following an airbus and a 757 in sequence. We were aware of those two aircraft and had visual on both. Weather was VFR; but getting dark. We were cleared to descend to 3;000 FT.We noticed a hit on our TCAS that was not pointed out by ATC nor made any radio transmissions that we heard. We looked for the traffic; but did not see anything. I actually thought it might have been a ghost hit. We were given a vector to a base leg. While in the turn and leveling off at 3;000 we received an RA. There was an aircraft in our path we could not see (we were looking and I now think he was climbing). We complied with the RA and received a 'clear of conflict' oral message. I immediately informed ATC that we had an RA and had to maneuver the aircraft to avoid collision. I inquired about the traffic. The Controller stated that we had plenty of clearance from the traffic. I was stunned. I felt like we were put in a very bad spot and the Controller did not have a clue. Maybe my bad for thinking a ghost target; but I still had very good SA [Situational Awareness]. We were constantly clearing outside and we were aware of the TA hit on TCAS. We did not know that aircraft's trends. We eventually were within 500 FT of the traffic. I am not saying I am perfect; however; my SA was pretty high. My concern is that we were put in a position that we should not have been put in. We were being vectored to final at one of the nation's busiest airports at night. ATC never pointed out the conflicting traffic. We had SA on hit on TCAS. Controller never said anything. After RA; Controller said 'traffic was not a factor'. I was so upset. I asked for his phone number. Captain called him last night. I could not. I was completely dumbfounded by what I heard and thought I was much too upset and angry to talk to a Controller with very low SA. This was not a good moment.


Second narrative: TCAS alert at 3;000 FT on approach into Boston.


Synopsis: While being vectored for an approach at BOS the flight crew of a B737-800 responded to a TCAS RA with an aircraft with which they never had visual conrtact. ATC advised there was no apparent traffic conflict. The First Officer was upset with the response which he believed failed to address what he believed to have been a near collision.