The air controller who was in charge of ill-fated Aeromexico Flight 498 told federal investigators Wednesday that he was working two positions, and has no memory of seeing any radar echo on his screen from the Piper Cherokee Archer II that collided with the DC-9 jetliner a mile above Cerritos on Sunday.
But National Transportation Safety Board investigators pointed out that there were at least six other radar echoes on the screen at the time of the collision, and added that it is "not unusual" for air controllers to do two jobs at a time.
Dr. John Lauber, who is in charge of the NTSB investigation, said he believes the Piper's echo was visible. Members of his team flew simulated missions Wednesday, duplicating the flight path of the Piper in the area where the collision occurred.
"Using an aircraft similar in all respects to the (Piper)," Lauber said, "we flew the path in three different profiles: With all on-board electronic equipment up and operating in mode C (with a transponder sending altitude readings), with the transponder sending the 1,200 code (the code normally transmitted when an airplane is proceeding by visual flight rules) and with the transponder on standby. . . ."
Each mission, he said, was clearly visible on radar.
"There was no problem seeing the aircraft in any mode," Lauber said, adding that this result appeared to confirm earlier digital readouts of the computer tapes from the air controller's radar.
Yet the controller apparently did not notice the echo.
"He does not recall a return from the (Piper) at all," Lauber said.
Asked how this could happen, Lauber said the controller had many other things to do at the time.
"We have data," he said, "indicating at least six other returns (echoes) in the area. Many other aircraft were involved . . . and we understand that he (the controller) was working both the radar and handoff positions."
This, he explained, means that while the controller's primary responsibility was still the monitoring of his own radar position and maneuvering the aircraft within it, he was also responsible for "handing off," or formally transferring control of various aircraft from his sector to adjacent sectors--a job that usually requires another trained expert.
But such a doubling-up is normal, Lauber said, during times of light air traffic--such as the minutes before noon last Sunday, when the jetliner and the private airplane met and plunged to earth.
Lauber said the air controller was able to do both jobs from his usual position.
"He didn't have to move from spot to spot to do it," the chief investigator said, "and he was fully qualified to handle both positions."
Asked what the air controller could have done, even if he had noticed the echo from the Piper, Lauber considered the question for a moment, and replied:
"Among other things . . . precisely what he did. Or he could have given a routine traffic advisory (as he did for another, similar, airplane spotted in the vicinity)."
Earlier, Lauber had said it now appears that the small airplane had violated air space restricted to commercial aircraft equipped with more sophisticated gear.
"The (Piper) was not operating with clearance," Lauber said. "It was not operating within regulations."
Have Tracked the Piper
Investigators now say they have tracked the Piper, carrying pilot William Kramer, 53, his wife and a 26-year-old daughter, from the point of the collision back to the point where it entered the restricted air space.
Lauber said the Piper entered the restricted area about two minutes before the crash, and if the pilot had seen the jetliner, "two minutes would have been plenty of time" to avoid a collision.
Investigators said they have established the fact that the Piper had its strobe lights and landing lights on--a common practice of small planes to increase their visibility to other aircraft in busy areas.
Lauber said the field phase of the investigation is now "winding down," and he expects to return to Washington by the end of the week. Experts there, he said, appear to have obtained "good data on all four channels" of the DC-9's flight data recorder.
This would include information on the jetliner's air speed, heading, altitude and vertical acceleration at the time of the collision--all data that Lauber said could be "critical" to determining the cause of the crash.
'Series of Failures
In the end, however, he admitted that he does not expect to find a single cause for the disaster.
"An accident," he said, "only happens because of a . . . series of failures."
Meanwhile, in Long Beach, experts zeroed in on the shattered tail section of the Aeromexico DC-9 and the twisted wreckage of the Piper, struggling to determine the cause of their disastrous encounter.
"The focus is on these pieces," said structural engineer John White, who heads the National Transportation Safety Board's wreckage inspection effort, "because this is where we have evidence that two airplanes came in contact.