In the minutes before Pan Am Flight 759 took off from New Orleans' Moisant Airport and crashed July 9, controllers and taxiing pilots consulted repeatedly about rapidly shifting winds, but none of the pilots decided to cancel their flights, according to tape transcripts released yesterday.
The crew of the Pan Am Boeing 727 and other airplanes seemed anxious to get the latest weather reports.
"What's your winds now?" a Pan Am crew member asked the tower about 10 minutes before the fully loaded plane took off. "Say your winds right now," a Texas International pilot instructed the tower shortly afterward.
The transcripts, released by the Federal Aviation Administration, show that controllers issued at least four warnings that sensors had detected wind shear, a rapid and potentially dangerous shift in wind speed and direction that many investigators believe may have played a role in the crash.
The tower reported shear in all directions around the airport 6 1/2 minutes before the accident. "We have, ah, low level wind shear alerts in all quadrants," the controller said. "Appears to be a frontal storm passing overhead right now. We're right in the middle of everything."
Ten minutes before the crash, the pilot of a plane landing on Runway 10, which the Pan Am jet used, told the tower, "You got a 10-knot wind shear on one zero Runway 10 at two hundred feet." That pilot's message was passed onto other planes in the area.
After the Pan Am reported, "Clipper 759 is ready," the jet was cleared for takeoff at six minutes after 4 p.m. A crew member repeated the clearance instructions in acknowledgment, the plane's last transmission. Thirty seconds after liftoff the plane slammed into a neighborhood of single-story brick homes less than a mile beyond the runway, killing 154 people.
Federal investigators are still trying to determine precisely what weather information the crew received. The plane's cockpit voice recorder has shown that at least two warnings about wind shear from the tower were picked up by the 727's cockpit radio, though whether the crew heard and understood them remains unclear.
Pilots say that, under current practices, shear alerts are not a prohibition on takeoff, but one more piece of information to use in deciding to go or wait. Many pilots say they place more weight on reports from planes that have just passed through an area than on the sensors' readings.
The crash investigation, led by the National Transportation Safety Board, is expected to examine these practices closely. Investigators are concerned that sensors installed to warn of wind shear and prevent accidents were working well but did not prevent the crash (if wind shear was in fact to blame).
The transcript shows, however, that a Southwest Airlines pilot, citing wind conditions, asked that he be allowed to use another runway. The tower granted the request.
The transcripts also raise questions of whether controllers were following alert procedures that day to the letter. Regulations say that when sensors alert controllers to wind shear, controllers should broadcast a warning.
However, the transcript suggests that in most cases controllers gave the information only in response to pilots' queries. And in some cases, they did not provide specific speeds, as the regulations call for. An FAA spokesman refused comment while an investigation is in progress.
The transcripts also provided a poignant account of the tower's discovery that the plane had crashed.
At about 4:09, apparently having seen the jet lift off the runway, the tower controller routinely instructed the plane to contact the radar room on another frequency. "So long," the controller said.
A minute later, the controller asked the radar room, "Talking to clipper?" as Pan Am planes are called. ". . . You talking to him?" The radar controller responded, "No." By this time, the plane had already crashed.
The plane failed to answer further calls. The radar room asked, "Where is he?" The controller responded, "I don't know. He took off of Runway 10 and we don't see the tag radar blip and we don't see anything out there that's probably him."
News of the crash apparantly reached the tower just after that. An American Airlines pilot radioed in saying, "You're aware he's down, aren't you?"
"Yeah, we got the equipment," the controller responded, an apparent reference to dispatch of emergency equipment.