Extract from "Air Safety Week" issue dated 31 May 04
Big sky – little sky
This tragic case should end the “big sky” notion that the air traffic controller’s ultimate savior will be the vastness of the airspace and the smallness of the airplanes. Satellite navigation accuracy, RVSM and automated, computerized flight controls have combined to kill the big sky theory. Dense clusters of airplanes headed in both directions and separated by half the 2,000-ft. vertical separation of yesteryear can make the sky along preferred tracks very small. Constructing a mid-air collision is now as straightforward as putting two trains on one set of tracks. In this accident, the controller tried to close the switches after the locomotives had passed by on their intersecting tracks. Technical refinement of navigational tracking accuracy and height-holding precision has increased the efficiency of preferred airspace use, but at an increase in the risk of mid-air collisions. Controllers now need to become sensitized to the “small sky” theory. For pilots, there is a reason why the “see and avoid” principle of collision avoidance may not be sufficient.
The ‘strange attractor’
For pilots, sighting the threat can lead to a greater hazard that might be called the “strange attractor.” This term describes a scenario where two pilots at night without a defined horizon become fixated on keeping each other’s lights in sight. In this mid-air collision, note that the TU154 changed its heading from
264º to 274º about two seconds after sighting the B757. The result can be a mutually maintained constant relative bearing on each other, which can greatly increase the risk of collision or near-miss. The control inputs by both pilots in the last few seconds tends to bear out the sudden arousal of imminent collision as
each “target” blossomed in size.
The two crews had been "visual" for almost 30 seconds. That is a long time in aerospace terms. Pilots disregarding a coordinated TCAS RA while attempting visual avoidance do so at their peril.