The National Transportation Safety Board ruled yesterday that air traffic control procedures contributed to the midair collision between a Pacific Southwest Airlines jetliner and a small plane that killed 144 people last Sept. 25.
That contribution came, the board said, because the PSA Boeing 727 and the small Cessna 172 were assigned headings by air traffic controllers that put them on "possibly conflicting tracks," and then were instructed to see and avoid each other.
The board also affirmed its tentative key finding of Thursday that the PSA flight crew members were primarily responsible for the San Diego disaster because they failed to keep the Cessna in view and further failed to ask for assistance from controllers after they lost sight of it.
That ruling infuriated pilots' groups. J. J. O'Donnell, president of the Air Line Pilots Association, charged that "the board has taken the easy way out. It is laying primary blame on the dead flight crew when in fact it is the system that is at fault. . . ."
Roger Crim, of the Soughwest Flight Crew Association, which represents PSA crews, said the ruling was "disgusting" and that the evidence gathered during the investigation showed that "the system broke down."
The safety board came within one vote of agreeing with Crim; several efforts to place more blame on the air traffic control system and some blame on the two men in the Cessna failed on 2-to-2 votes. One position on the five-memebr board is vacant.
The board rejected suggestions that the following factors should be listed as contributing to the crash:
The Cessna, for some unexplained reason, changed its assigned course by 20 degrees. According to experts, had the Cessna continued on its assigned heading, it would have passed behind the PSA jet.
Lack of discipline on the flight deck of the PSA jet. The cockpit voice recording showed that the crew members engaged in casual conversation with each other and two visitors who were riding in the extra flight deck seats. However, the extraneous talk ceased in the final moments of the flight as the crewmembers looked around for the Cessna.
The fact that, at the time of the collision, the Cessna was communicating with one air traffic control center on one frequency while the Boeing was communicating with the An Diego tower on another frequency. Therefore, neither controller could talk to both planes at the same time.
The failure of the controllers to restrict the Boeing to an altitude of 4,000 feet until it had passed through the airspace assigned to a small nearby airport.The lack of such restriction was found to be common practice at San Diego, even though the restriction was required by a letter of agreement between the San Diego tower and the nearby airfield. If the Boeing had stayed at 4,000 feet, some reasoned, it would not have hit the Cessna. The collision occurred at about 3,000 feet.
Board member Francis H. McAdams, who pushed for those four points and several others, said that he would a file a dissenting opinion to the majority report on the cause of the accident.
The San Diego accident raises once again the question of whether airline pilots should be permitted to rely on their own eyesight to separate their planes from others. Such separation, called "see and avoid," has been a controversial subject for years, and there have been several collisions involving "see and avoid" conditions.
The board has recommended that the see and avoid concept not be used except for a plane trailing another with both on final approach to a runway. Planes making other kinds of aneuvers in the same area - as the Cessna was doing on that September day - should be separated from airliners another way, the board has urged. The Federal Aviation Administration has said it will act soon on those recommendations.