Date: 201808
Local time of day: 1201-1800
Location: NCT.TRACON, CA
Flight conditions: VMC
Light: Daylight
Aircraft: Large Transport
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Initial Approach
Airspace: Class B NCT
ATC / advisory: TRACON NCT
Second aircraft: Heavy Transport
Reporter organization: Air Carrier
Reporter function: Pilot Flying; First Officer
Reporter qualification: Flight Crew Multiengine; Flight Crew Air Transport Pilot (ATP); Flight Crew Instrument
Human factors: Confusion; Situational Awareness
Second reporter function: Pilot Not Flying; Captain
Anomaly: ATC Issue All Types; Conflict Airborne Conflict; Deviation - Speed All Types; Deviation / Discrepancy - Procedural FAR; Inflight Event / Encounter Unstabilized Approach
Detector: Automation Aircraft TA; Person Flight Crew
When detected: In-flight
Result: Air Traffic Control Issued New Clearance; Flight Crew FLC Overrode Automation; Flight Crew Requested ATC Assistance / Clarification; Flight Crew Became Reoriented
Contributing factors: Airspace Structure; Human Factors; Procedure
Primary problem: Procedure

Narrative: While on the Arrival to SJC; we briefed a RNAV Z Runway 12L; visual conditions prevailed. When we checked in with Approach we were given clearance to do the approach. I was in VNAV and dialed the FAP in the altitude window. While approaching HITIR waypoint; Approach warned us that an Aircraft Y will be sequenced behind us and to let us know if and when we get the aircraft in sight. The Pilot Monitoring saw the Aircraft Y and told Approach that we indeed had it in sight. This was the first threat; as we were on VNAV path for the approach I noticed that the Aircraft Y had absolute no relative motion with us; at this point ATC gave us instruction to maintain visual separation. As we continued the approach I told the Pilot Monitoring that the aircraft was getting too close for comfort; the Pilot Monitoring then said 'well let's take appropriate action.'It was at that time; I clicked off the autopilot and decided that it was better to start an abrupt descent and get out of his altitude and start a turn to the east to get behind him and out of his altitude. A TA was then given; but no RA. I descended to 3000 feet. The Pilot Monitoring told Approach that the approach was not going to work and then ATC told us to 'be cleared now to 2000 feet and cleared for the Visual Approach.' At that point I was in no doubt in the yellow trying to hand fly the aircraft while keeping the Aircraft Y that was now above us and to the right. After stabilizing the aircraft I tried to engage the autopilot again; but had no luck due to the MCP panel not being set for engagement. I then just flew the aircraft by hand and conducted a Visual Approach and landed without further incident in front of the Aircraft Y.ATC should have never given us an approach clearance while knowing that we were converging with the heavy. Telling Approach that we had the Aircraft Y in sight; put the liability on us to keep separation. It added to the already heavy task loading during the approach phase. While descending to get out of the converging path I exceeded the 250 knots under 10;000. I believe that this was the best course of action to eliminate the threat that was coming. I may have made sure that the thrust levers were at idle.


Second narrative: [Report narrative contained no additional information.]


Synopsis: Air carrier flight crew reported exceeding 250 knots in order to remain separated from an aircraft conducting an approach to a parallel runway.