A B737 crew reported climbing with ATC clearance to 17;000'. Crossing traffic at 16;000' was sighted but the reporters were unable to determine traffic separation altitude and leveled at 15;200' in response to a TCAS RA.
Synopsis
A B737 crew reported climbing with ATC clearance to 17;000'. Crossing traffic at 16;000' was sighted but the reporters were unable to determine traffic separation altitude and leveled at 15;200' in response to a TCAS RA.
Narrative
We were approaching JUMPR intersection from the north and had been cleared to 15;000'. Boston Center informed us that we would get cleared higher when past an Airbus that was east of us at 16;000' and converging. We both saw the Airbus on what appeared to be a parallel ground track. We reported the Airbus in sight and Boston cleared us to climb to 17;000' and maintain visual separation. As we continued to climb; I realized that the Airbus was stationary in the side window and getting closer. About the time I suggested to my First Officer that we level off below his altitude; we got a TCAS RA aural warning directing us to monitor vertical speed and visual display showing us to maintain level flight or descend. We stopped climbing and leveled off at 15;200'. We reported to Boston that we had leveled off; that we had been responding to an RA; and that our intention was to maintain our altitude until we had passed behind the other aircraft. We passed a couple of hundred yards behind and about 800 feet below the Airbus soon afterwards. Once clear on the left side of the Airbus; with a diverging vector; we continued our climb to 17;000'. The Boston Center Controller asked us how close the RA had been and I answered '800 ft below.' He said 'no problem' and shortly cleared us for an early turn on course. In light of the difficulty of estimating range visually to another aircraft; we should have monitored the map display to assess lateral separation and lateral closure. That would have indicated to us that we should have shallowed out our climb to let the other aircraft pass across our nose and to increase lateral separation before climbing through within 1000 feet of its altitude.
Second reporter narrative
Boston Center called out Airbus traffic at 10 o'clock level at 16;000'. Both Pilots saw the traffic and told ATC traffic in sight. Boston Center then called us out to the Airbus. Airbus Crew called us in sight. Boston told Airbus we will be climbing through his altitude to 17;000'. Boston then cleared us to 17;000'; maintain visual separation with the Airbus. I put 17;000 ft into MCP altitude. Autopilot engaged with autothrottles and VNAV. Our flight path was taking us behind the Airbus. I don't remember what our VVI was; and passing 15;000' we got an RA. I disengaged autopilot/autothrottles; followed RA guidance; and descended 200 ft to 15;000. Captain advised ATC that we leveled off at 15;000' to stay below the Airbus. At 15;200' we had 800 ft vertical separation from the Airbus. RA cleared shortly after leveling at 15;000 ft. We then continued our climb to 17;000'. Captain and I could have done a better job of communicating the relative position of the aircraft and our current climb rate in VNAV before I placed 17;000' in the MCP. In hind sight; that evaluation may have led to coming out VNAV into V/S to better control the climb rate.
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Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.