Date: 201708
Local time of day: 0601-1200
Location: ZZZ.TRACON, US
Flight conditions: VMC
Light: Daylight
Aircraft: B737-700
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Initial Approach
Airspace: Class E ZZZ
ATC / advisory: TRACON ZZZ
Second aircraft: Skyhawk 172/Cutlass 172
Reporter organization: Air Carrier
Reporter function: Captain; Pilot Flying
Reporter qualification: Flight Crew Air Transport Pilot (ATP)
Second reporter function: Pilot Flying; Single Pilot
Anomaly: ATC Issue All Types; Conflict NMAC
Detector: Automation Aircraft TA; Automation Aircraft RA; Person Flight Crew
When detected: In-flight
Result: Air Traffic Control Provided Assistance; Flight Crew FLC complied w / Automation / Advisory; Flight Crew Took Evasive Action
Contributing factors: Airspace Structure; Procedure
Primary problem: Procedure

Narrative: On approach was given 210 knots and 3000 ft until ZZZZZ; clear approach. Then we were told to hold 170 knots until ZZZZZ1. We started to descend to 2400 ft past ZZZZZ. Then ATC ask our altitude and told us to go 2800 ft in the same sentence for traffic. Then we were given 2500 ft for traffic; and told traffic alert; which we did and then got a TA; visually acquired the traffic and executed 'see and avoid' to ensure there was no conflict. ATC asked if we had the airport and then clear for the visual. It was a lot of instructions in a less than a minute. We continued on to the airport and still maintained SA (Situational Awareness). We were on profile and landed with no other issues.


Second narrative: My altitude of 3;500 MSL is exact as indicated on my correctly set altimeter. The separation of 300 vertical feet is as was indicated by the TCAS in my aircraft and appeared correct visually. The 500 feet of horizontal separation is an estimate. I was flying VFR in VMC; was not on a flight plan and was squawking 1200 with a properly working Mode C transponder. I was flying the appropriate VFR altitude for my heading of 0 to 179 degrees.I received a traffic alert from my TCAS indicating traffic at my 12 o'clock and 300 feet below me. I began to visually look for the traffic and within seconds realized that I was on a collision course with a B737. The traffic appeared to be moving at an estimated 300+ knots. The 737 did not seem to adjust their course or altitude to create additional separation from me. It did not appear to me that they ever saw me. I would also have to assume that ATC never provided them a traffic advisory as to my position or they never heard the transmission if there was one. Additionally I would also have to assume that they did not receive a traffic advisory from their onboard technology. I was not on an approach frequency but it most certainly appears as though there were multiple failures or breakdowns that allowed the 737 to get so close to me. Additionally; all of the other airline traffic in the area was 1;500 feet above me; well into the Class Bravo airspace. I fly in this area on a regular basis and I have never seen an airliner (or any other fast moving jet) at 3;200 feet MSL.If the approaching aircraft was another slow moving C-172 there would have been considerable time to alter course and or altitude. However; given the speed of the 737 it went from a barely visible spec in the sky to a serious threat in a matter of moments.


Synopsis: A B737 flight crew and a Cessna 172 pilot reported a near collision and late instructions from ATC.