Radar and voice communication records indicate that the pilot of an Aeromexico DC-9 had been warned that there was a small airplane in his vicinity and may have been taking evasive action at the time the two aircraft collided, federal investigators said Tuesday.
Dr. John Lauber, who is in charge of the National Transportation Safety Board investigation into the catastrophe over Cerritos on Sunday, said an air controller warned the DC-9 pilot of "traffic at 10 o'clock, one mile northbound, altitude unknown" a little more than a minute before the crash.
The jetliner's pilot acknowledged the warning, Lauber said, and was told to reduce his speed to 170 m.p.h.--but was not given permission to change course.
Both Banking Left
Eyewitnesses questioned by NTSB investigators, however, all agreed that the DC-9 and the single-engine Piper Cherokee Archer II were both making steep left banks at the time they collided, a maneuver that experienced pilots said the airliner would not have made without permission except in an emergency.
Lauber said his information came from the initial readout of digital tapes from Los Angeles Terminal Approach Control (TRACON) radar and from voice recordings of the conversations between the air controller and the airliner.
He said Aeromexico Flight 498 had contacted Los Angeles TRACON and received instructions for a routine instrument landing approach when the air controller spotted the Piper.
He said the small plane's transponder--an on-board radio transmitter that amplifies radar echoes to make them more easily identifiable--was tuned to a code that is normally transmitted only by airplanes that are proceeding by visual--rather than instrument--flight rules.
But the transponder was not transmitting the Piper's altitude, he said, and this made it impossible for the air controller to be sure whether it had invaded the tightly regulated terminal control area (TCA) that extends from 6,000 to 7,000 feet in that area.
Lauber said he is reasonably sure the blip seen by the controller was from the Piper.
"That transponder return," he said, "ends at the same time the readout ends from the Aeromexico plane. Its flight path is generally consistent with the planned flight path of the Piper Cherokee . . . and therefore it is reasonable to assume that this was the airplane that subsequently was involved in the collision."
The Aeromexico pilot acknowledged the air controller's warning, saying "Roger, 498 (the flight's number-designation)" and was told to reduce speed and begin descending from 7,000 to 6,000 feet.
Then, Lauber said, another small airplane--a "pop-up target" whose on-board transponder also was tuned to the visual flight code--appeared on the screen and asked for a traffic advisory. The air controller gave the "pop-up target" a new transponder code (to identify it as an instrument-controlled flight in the area) and ordered it to make turns and altitude corrections to keep it out of the path of other aircraft.
When he tried to re-contact Aeromexico 498, there was no response.
"He made eight attempts," Lauber said. "But radar data shows the transponder return from the DC-9 stopped at 6,500 feet; right smack in the middle of the TCA sector."
Lauber said the Piper initially collided with the DC-9's left wing and then tore into the stabilizer, causing the jet to flip upside down. Witnesses have said the jetliner plunged to earth in that position.
The stabilizer, which controlled the jet's pitch or nose-up, nose-down movement, was sheared off in the collision, Lauber said, "and once that happened, no control was possible."
Lauber said the digital readouts and voice recordings--and data now being retrieved from the jetliner's own voice recorder and flight recorder--will be integrated later into the investigation to develop "a complete report" on exactly what happened over Cerritos, 20 miles southeast of Los Angeles International Airport.
Meanwhile, there were these developments:
Test for Drugs
Lauber said a blood sample--for drug testing--was taken Tuesday from the air controller who was handling the DC-9 at the time of the collision. But he said he had no real suspicion that drugs had in any way been involved in the crash.
He also largely discounted early reports from the Los Angeles County coroner's office indicating that the pilot of the Piper Cherokee had suffered a heart attack just before the aerial collision.
NTSB spokesman Ira Furman identified the pilot as William Kramer, an executive who moved to Palos Verdes from Spokane, Wash., about a year ago. He said Kramer had held a private airman certificate (pilot's license) for about six years, had more than 200 hours of flying experience and had undergone a routine flight physical before moving from Spokane to Palos Verdes.
At that time, he added, there appeared to be no indication of heart disease.