Flight Crew Air Transport Pilot (ATP)
Flight Crew Last 90 Days 90; Flight Crew Total 13900; Flight Crew Type 2000
Situational Awareness; Physiological - Other; Confusion
Conflict NMAC
Flight Crew Took Evasive Action
Procedure; Human Factors; Airspace Structure
Approximately 6 NM prior to our NMAC we were issued VFR traffic at 12 o'clock; opposite direction; maintaining 4;500 FT MSL. Our TCAS confirmed the approximate location of the issued target and of an aircraft indicating 500 FT ABOVE our altitude of 4;000 FT MSL. Shortly after the traffic was issued; we obtained visual contact with a single engine Cessna type aircraft and advised the Controller that this traffic was in sight. At a TCAS range of 2.5 NM; suddenly and without ANY indication from the intruder aircraft; we observed the nose of the Cessna pitching rapidly down (10-15 degrees) and rolling slightly to his right. We received an RA to descend; followed immediately by an RA to increase descent. As the intruder aircraft disappeared under the nose of our aircraft; we received a climb RA. We responded to the climb RA and advised New York Approach of the RA maneuver. It is my firm belief that had we initially responded to both descent guidance commands we would have not been able to avoid the Cessna vertically. The only reason that descent guidance was not followed was that we had that aircraft in sight and realized he was committed to an unwarranted extreme avoidance maneuver of his own. After receiving a clear of conflict advisory; I requested an explanation from the Controller who queried the Cessna pilot for a reason for his action. It was at that point that I realized he was actually being flight followed by New York Approach and in contact with that Controller. The pilot of the Cessna stated that we 'appeared to be at his altitude'. The Controller responded; 'Sir you just dove through his altitude'. In this instance; 'see and avoid' proved to provide the only fail-safe method of avoidance. The pilot of the other aircraft who was operating VFR and maintaining an appropriate VFR altitude elected to maneuver contrary to his originally correct orientation without verifying with the Controller flight following him of our altitude assignment.
A close encounter--the result of authorized 500 FT vertical IFR/VFR separation--turned into an NMAC when the pilot of a light plane; apparently believing their altitudes to be equal; initiated aggressive avoidance maneuvers with respect to the reporter's Global Express. The reporter expressed his belief that; based on his visual observations; the initial TCAS RAs which resulted would have aggravated the event.