Page:CAB Accident Report, Eastern Air Lines Flight 663.pdf/21

Rh thousand feet on top of Pan American", and by the fact that he was never advised to the contrary by the DR-1 controller. That vertical separation was being aimed for is also implied in the DR-1 controller's testimony in explanation of the basis on which he issued EAL 663 the turn to 090 degrees. He stated the turn was "to maintain at all times more than three miles horizontal separation from the Pan American -Clipper. I believe that is why I gave him a heading of 090 degrees at the same time to give the aircraft a chance to continue his climb." The Board believes that as the situation developed, vertical separation in the order of 1,000 feet did in fact exist between the aircraft when they were about 3 miles apart, but this was unknown to the controllers. This is because in order for the DR-1 controller to provide this separation it was necessary for him to receive reports originating from the aircraft which would assure him that they were, and would continue to be, separated vertically by at least 1,000 feet and this information was never received. For the same reason the Board is unable to reconcile the statement of the DR-1 controller, in his call of traffic for EAL 663 "below you", as being more than an assumption since the last information received by him relative to PAA 212 was that it was leaving 4,500 feet. Below is a tabulation showing in chronological order the transmissions to and from each of the aircraft regarding altitude, together with corresponding altitude values derived from the PAA flight data recorder and the reported or computed altitudes of EAL 663.

As the tabulation shows, at the moment of the traffic call to EAL 663, PAA 212 was approximately 250 feet below EAL 663's altitude. This vertical distance, however, would be considerably less than the 1,000 feet or more that a pilot would normally expect in consequence of a call of known traffic as "below you."

The Sperry Gyroscope Company Study previously discussed noted that in test runs in which a vertical miss vector of 250 feet was present at an initial range