Date: 201401
Local time of day: 0001-0600
Location: ZBW.ARTCC, NH
Flight conditions: VMC
Aircraft: B737 Undifferentiated or Other Model
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Flight phase: Cruise
Airspace: Class E ZBW
ATC / advisory: Center ZBW
Second aircraft: Cessna Citation Undifferentiated or Other Model
Reporter organization: Air Carrier
Reporter function: First Officer; Pilot Flying
Human factors: Situational Awareness; Training / Qualification
Second reporter function: Captain; Pilot Not Flying
Anomaly: Conflict Airborne Conflict; Deviation / Discrepancy - Procedural Published Material / Policy
Detector: Automation Aircraft TA; Automation Aircraft RA; Person Flight Crew; Person Air Traffic Control
When detected: In-flight
Result: Air Traffic Control Issued Advisory / Alert; Flight Crew Took Evasive Action
Contributing factors: Aircraft; Human Factors; Procedure
Primary problem: Human Factors

Narrative: While on an IFR flight plan [along the east coast] a near mid-air collision occurred during cruise flight. ATC alerted us to VFR jet traffic; a Cessna Citation; at our approximate 11 o'clock position about 10 miles; descending through our altitude. We were told the traffic had us in sight and would maintain visual separation from us while descending through our altitude. Because we were cruising below the FL180 transition level; we still had all of our external lights illuminated for safety. We reported traffic in sight and noted to each other that the traffic was indeed slightly above us with TCAS indicating a descent. Our cruise speed was 280 KIAS. Assuming the Citation was descending at approximately the same speed; our closure rate was in the neighborhood of 700 KTAS. This means our two aircraft were closing the distance between us at about 5.1 seconds per mile; giving us a little over 50 seconds from the initial ATC call before our aircraft would be over the same spot. Very shortly after the Controller called out the traffic to us; maybe 10-15 seconds; we received a TA from our TCAS. We were monitoring the opposing aircraft both visually and on our TCAS display in the cockpit. A few seconds later; as the opposing aircraft continued its descent directly at our aircraft; our TCAS issued an RA with instruction for us to descend. Because we were monitoring the other aircraft so closely; I almost immediately verbally and physically initiated a climb by pushing the throttles toward the forward stop and raising the nose to 20-25 degrees nose up; similar to a terrain avoidance or windshear escape maneuver. I also made a slight offset to the right to help increase our distance from the opposing aircraft. Within seconds; TCAS showed the opposing aircraft passing directly beneath us with between 200-300 feet of vertical separation. At somewhere around 60-65 tons; initiation of a climb or descent will be met with a momentary lag before a change is realized in aircraft position. Despite the lag; I was able to create vertical separation with the climb; which eventually registered approximately 3;500-4;000 FPM. We eventually topped out at 17;800 feet after less than 30 seconds of climb. It is my professional opinion that initiation of a descent as directed by the TCAS RA would have resulted in a mid-air collision. The RA came as the opposing aircraft was maybe 1.5-2 miles from us and approximately 100 feet above our altitude; continuing its descent through our level altitude. With less than 10 seconds closure remaining and the other aircraft actively descending; a descent on our part would have had to yield several thousand fpm almost immediately for us to beat the opposing aircraft to a lower altitude where we could have safely passed underneath. Before the RA; as we watched this scenario begin to unfold over about a 12 second period; it became obvious to me that a rapid climb was going to be our best escape route; and that is why I flew opposite the RA command in the cockpit. At no time did airspeed decay to an unsafe level. I never saw our speed go below 260 KIAS. The Captain immediately communicated our deviation to ATC (no doubt with my colorful commentary bleeding through in the background) and coordinated a descent back to our originally assigned altitude. We reestablished ourselves on course and continued on to an uneventful approach and landing with no further incident.


Second narrative: While level at our cruise altitude of 16;000 feet; ATC called out VFR traffic at 12 o'clock ahead approaching head on to us. The traffic was in sight with landing lights on. Because of our cruise altitude our landing lights were on as well. The traffic called us in sight; as we called them in sight. The traffic had been in a VFR descent and stopped at 17;000 momentarily; as seen on out TCAS. At approximately 7 miles in front of us the traffic began descending below 17;000 feet. When our TCAS alerted to RA; the traffic was showing 300 feet below us and called for a DESCEND NOW Command. Both the First Officer and myself at about the same time realized this would definitely have put our aircraft in a dangerous position as we would have been descending down on top of the descending traffic. I believe I said CLIMB right as the First Officer initiated a climb away from the traffic which increased separation significantly. I notified ATC of the RA Climb; and we leveled off at 17;800. ATC then asked if the traffic was head on and how close? I was convinced had we not climbed our separation would have been minimal.


Synopsis: B737 fight crew at 16;000 feet reports a NMAC with a VFR Cessna Citation descending in the opposite direction. Each aircraft had been advised of the others presence by ATC and each had reported the other in sight. The Citation continued to descend into the B737 generating a TCAS descend RA for the B737 crew; which the flying First Officer with the Captain's concurrence; chose to ignore and climb vigorously.