Pilots of a Republic Airlines DC9 that took off from New Orleans about five minutes before the Pan American World Airways jet that crashed last Friday said that their plane encountered severe runway winds and that its stall-warning device activated at liftoff, a National Transportation Safety Board spokesman said last night.
Crew members of Republic Flight 632 to Memphis told board investigators that they managed to raise the landing gear and gain speed after leaving the ground. As they moved away from the airport, they radioed a message to controllers about the strong winds but apparently did not mention the stall warning.
Investigators said it is not clear how, if at all, controllers in the tower at New Orleans International Airport followed up the pilots' radioed warning or whether it was heard by Pan Am Flight 759, which was preparing for takeoff on another runway at the time.
Pan Am's fully loaded Boeing 727 took off shortly after 4:06 p.m., about five minutes after the Republic plane, and crashed after about 30 seconds in the air, killing 146 passengers and eight persons on the ground in a residential area of suburban Kenner, La.
The Republic crew's report could support the theory now dominant among investigators that "wind shear," violent changes in wind speed and direction, played a major role in the crash.
Stalls occur when air is not moving fast enough over a plane's wings to keep it in the air. That can happen when wind speed changes suddenly.
A stalling plane is actually falling out of the air, and commercial jets are equipped with "stick shakers," devices that rattle the main control stick to warn pilots that the plane will stall if speed is not increased.
Pilots say activation of the stick shaker, as happened aboard the Republic DC9, is unusual and serious, especially at low altitudes where a plane has little chance to recover from any loss of control. Two pilots interviewed last night said they had experienced stick shakes but were able to fly out of them.
Last Jan. 13, the shaker aboard Air Florida Flight 90 activated as the jet lifted off from National Airport. The plane remained airborne for 30 seconds before striking the 14th Street bridge and plunging into the Potomac River, killing 78 people.
Investigators are still trying to determine precise weather conditions at the time of the Pan Am crash. Twice within minutes before the plane took off, wind shear detection devices operated by the airport had picked up signs of the condition. These warnings were broadcast over two frequencies, investigators say, but it remains unclear whether the Pan Am crew heard them.
A severe storm was reported southwest of the airport, and controllers have said that visibility was about two miles, with rain falling, shortly before the accident.
The pilot and co-pilot of the Republic jet told investigators they took off heading south. About one-third of the way down the runway, they said, they ran into sheets of rain. Then they noticed unusual fluctuation in the plane's air speed, which may have been caused by rapid changes in the speed or direction of air around the plane.
As the pilot put the plane's nose up for liftoff, the stick shaker sounded. "They got off the ground and got the gear up and their airspeed increased," the spokesman said.
After that, the plane climbed normally, and the pilots sent a brief message back to the tower saying they had encountered wind shear on the runway.
Meanwhile, federal officials yesterday were wrapping up field investigation of the accident. The plane's engines have been sent to a Pan Am facility at Kennedy Airport in New York, where they will be stripped to see if they malfunctioned on takeoff.
Safety board technicians here continued to work on decoding the plane's two flight recorders.
A spokesman for the Jefferson Parish (county), La., coroner said yesterday that the bodies of 98 crash victims have been identified.