The Aeromexico Disaster--Gathering Clues in the Search for Answers : THE QUESTIONS: At a Glance, What’s Known and What Isn’t

National Transportation Safety Board investigators know a lot of things about the collision of a Piper Cherokee Archer II and an Aeromexico DC-9 jetliner over Cerritos last Sunday.

There is a lot of things that they do not know, too. And there are some things they may never know.

The airliner--what is known:

Aeromexico Flight 498 was preparing for a landing at about noon at Los Angeles International Airport after a flight from Mexico City that had included stops at Guadalajara, Loreto and Tijuana. On board were 58 passengers and a flight crew of six, including flight Capt. Arturo Valdez Prom, an experienced jet pilot whose professional records indicate a high degree of competence. Preliminary data indicate that the aircraft was in good operating condition.

At about 11:52 a.m., while heading roughly northwest, Prom received clearance from air traffic controllers to make his approach to LAX runway 25L and was told to reduce his speed to 190 knots and descend from 7,000 to 6,000 feet through the southeastern sector of the airport’s Terminal Control Area--a restricted approach zone through which aircraft are not authorized to pass without specific permission from controllers.

The light plane--what is known:

The Piper took off from Torrance Airport at about 11:40 a.m. after the pilot, William K. Kramer, 53, filed a plan for a flight to Big Bear Lake. With Kramer were his wife, Kathleen, 51, and their daughter, Caroline, 27. Kramer, a recreational pilot, had current navigational maps for the area, had recently been checked out to fly locally and had recently discussed the restricted TCA airspace with another pilot and with a flight controller in charge of the Torrance control tower.

Coroner’s officials said tissue from Kramer’s heart showed signs of occlusive heart disease. Preliminary data indicates that the plane was in good operating condition.

Kramer never requested permission to enter the TCA or otherwise contacted air traffic controllers. The little plane flew east at an unknown altitude after takeoff.

Air traffic control--what is known:

The DC-9 made its approach to LAX under the guidance of an experienced, qualified, 35-year-old air traffic controller at the Los Angeles TRACON approach-and-departure facility. (The name of the controller has not been released.) Recent tests show that while the control equipment was performing at acceptable levels, radar returns have been “relatively weak,” resulting in relatively poor resolution on the controller’s screen.

The controller had several radio conversations with the jet that included a warning about a light plane--not the Piper--in the DC-9’s area. Both the DC-9 and the Piper appeared on the controller’s screen--along with several other aircraft--but the data available on the Piper did not include its altitude. The controller had no conversations with the Piper and did not warn the DC-9 about the Piper; in the moments before the collision, the controller was busy with still another aircraft. At about 11:55 a.m., both the DC-9 and the Piper disappeared from radar data, at a time when the DC-9 was “smack in the middle of the TCA.”

The collision--what is known:

The DC-9 and the Piper collided roughly head-on. The nose wheel of the Piper struck the vertical stabilizer at the tail of the jetliner, a split second before the horizontal stabilizer atop the big jet’s tail sheared off the top of the smaller plane. Both aircraft plummeted earthward. The jetliner plunged in an inverted attitude and hit the ground upside down. The light plane fluttered to Earth about two blocks away.

What is not known:

Researchers have yet to complete tests that should show conclusively whether Kramer, members of the Aeromexico flight crew or the controller were under the influence of alcohol, drugs or medication.

Experts at the National Transportation Safety Board headquarters in Washington have yet to complete a reading of the DC-9’s flight data recorder, which could indicate whether Prom saw the approaching Piper and attempted evasive maneuvers before the collision.

Preliminary radar data readouts and preliminary analysis of control center recordings and interviews with controllers have yet to show conclusively whether radar equipment was functioning adequately and whether controllers were performing their jobs properly. Further study is expected to provide better answers.

What may never be known:

Why the Piper strayed into the restricted TCA approach route could remain pure speculation. All three aboard the plane died in the accident, and the pilot is not believed to have had radio contact with anyone in the moments preceding the crash. There were no flight data or cockpit voice recorders aboard the plane.

Whether Kramer suffered a heart attack after takeoff may never be resolved. The Los Angeles County coroner’s office says Kramer suffered such an attack “within minutes before his death,” but pathologists say it is often difficult, if not impossible, to determine whether a person had suffered a heart attack within the last day of life--much less within minutes of death.

Whether the Aeromexico flight crew saw the Piper before the crash may remain a mystery. The DC-9’s cockpit voice recorder was severely damaged in the crash, and safety board officials say their experts are finding it “terribly difficult” to decipher the final conversations of the cockpit crew.