In the Sperry Gyroscope Company Study[1] one experiment was conducted to determine the effect of pilot warning indicators on the ability of the pilot to discriminate between aircraft on collision and noncollision courses. This experiment was conducted in the F-5l Gunnery Trainer at the PAA National Aviation Facilities Experimental Center. In this experiment, as the miss vector (distance between aircraft either vertically or horizontally) decreased, the frequency increased in which a decision was made that a collision course existed.
The evaluation of a target may depend on the observed angular velocity (sight line rate)[2] and the observed rate of change in angular subtense (range-rate)[3] rate of the target. If the sight-line rate of a target is well above the motion threshold the pilot can be fairly certain the target is on a non-collision course. However, if the sightline rate is below the motion threshold and there is a perceptible increase in apparent target size, the threat may be evaluated as a collies course.
Sight-line rates at final decision for courses judged as collisions by the pilots were about six minutes of arc per second regardless of the structure, or the miss vector, for vertical misses. For courses judged as misses (vertical miss vector) the line-of-sight rate was about nine minutes of arc per second. However, in these instances a horizon line was observable, and the pilots reported using this in addition to the "fixity of bearing"[4] criterion. For horizontal miss vectors of 1,000 feet (for which a reference line was not present) the sight-line rate was nearly 18 minutes of arc per second.
Near-Miss Investigation
On June 2, 1965, at approximately 2234 e.d.t., a B-707 and a DC-6 passed each other at 5,000 feet altitude in the vicinity of Freeport, New York. They were estimated to be separated by only 100 feet laterally at the time of passage.
The DC-6 was operating on an IFR clearance from Boston to JFK Airport After holding at the Deer Park VORTAC at 6,000 feet the flight was cleared to depart on the 228-degree radial. The B-707 had been cleared to 5,000 feet on a heading of 100 degrees after departing JFK Airport. The DC-6 flight was given traffic at 2 o'clock, four mites eastbound, and below.
The DC-6 flight crew all indicated that they saw the traffic and estimated that the B-707 was at or above their altitude and on a collision course. The captain of the DC-6 took evasive action by diving his airplane from 6,000 feet to pass below the B-707 at 5,000 feet. The B-707 flight recorder readout affirmed the aircraft's altitude of 5,000 feet.
- ↑ A study of requirements for a Pilot Warning Instrument for Visual Airborne Collision Avoidance. Sperry Gyroscope Company - December 1963.
- ↑ Sight-line rate is the observed angular velocity or relative movement of a target in a horizontal or vertical plane.
- ↑ Range-rate is the observed rate of change in angular subtense of a target or the rate at which the target appears to change in size as the range opens or closes.
- ↑ An apparent lack of relative motion of the observed target
