Federal investigators attempted Tuesday to determine if the weather phenomenon known as wind shear contributed to the crash of Northwest Airlines Flight 255, as the death toll in the disaster rose to at least 157--three of them on the ground.
At the same time, other investigators began poring over maintenance records of the jetliner's engines, which had been replaced several times in recent years as the result of problems.
However, a government aviation source said events preceding the crash suggest that the plane, ultimately headed for Orange County's John Wayne Airport, may have encountered a sudden down draft that deprived the craft of the lift it needed to take off.
Wind shear has been blamed for at least five crashes in recent years, including two of the worst--the crash of a Pan American jetliner after takeoff from New Orleans on July 8, 1982, killing 154, and the crash of a Delta Air Lines Lockheed L-1011 jumbo jet on approach to Dallas-Fort Worth on Aug. 2, 1985, killing 137.
Eyewitness accounts and evidence at the crash site here indicated that the plane, a twin-engine MD-80, had difficulty gaining altitude as it took off from Detroit's Metropolitan Airport. The plane yawed to the left and to the right, with flames spilling from its left engine, according to some witnesses.
The aircraft first struck a 41-foot-tall light pole less than 200 feet beyond the end of the runway--at a point where it should have already been hundreds of feet in the air.
"Right now, there is nothing from surface (weather) observations at the airport to lead us to believe there were low-level wind shear conditions," government aviation weather chief Charlie Sprinkle told The Times.
"Winds were not strong. There was no precipitation. No lightning. No visual clues," said Sprinkle, head of the National Weather Service aviation branch in Washington.
But Sprinkle said investigators had yet to analyze data from the six computer-linked wind shear sensors at the airport.
Wind shear, an often invisible phenomenon, occurs when adjacent masses of air move in different directions. The condition frequently results in "microbursts" during which columns of air descend rapidly before mushrooming out on impact with the ground.
A plane taking off into a micro-burst would encounter an assortment of conflicting wind conditions.
First it would hit head winds that would increase the lifting effect of its wings. Then it would encounter strong down drafts pushing the plane downward. Finally, it would pass through tail winds that would decrease lift.
"The plane rolled left and right, it wasn't gaining altitude," an aviation source said. "And what air controllers thought was a fire may have been a compression stall in the engine," the source said.
A compression stall, which can result in flames shooting out of baffles in jet airplane engines, occurs when the flow of air into the front of the engine is interrupted. This can happen on takeoff when the nose of the airplane lifts unusually high and the engine cannot take in the optimum amount of air.
When that occurs, pressure in the compressor is diminished and flames shoot forward from the main combustion chamber, exiting through the baffles.
A Federal Aviation Administration source said the flames can sometimes create a false impression that an engine is on fire.
Possibility Still Open
Reports by some observers that the plane's left engine was on fire as it took off led investigators to continue to examine the possibility that engine failure was a factor in the crash.
"Technically all airliners are certificated to take off even if they lose an engine on a critical point on takeoff," said Wally Mason, a Los Angeles-based captain with one of the nation's major air carriers. "Every pilot is trained to deal with this maneuver, but when it's a fully loaded airplane, you're pushing it right to the limit."
Both engines, along with other debris, remained at the crash site Tuesday as federal investigators continued to attempt to reconstruct how the disaster occurred.
The plane's left engine, charred and mangled, lay on the pavement of Middlebelt Road, hundreds of feet from where the aircraft crashed into a busy highway intersection. The plane's right engine lay in the grassy median strip of I-94, hundreds of yards from the point of impact and above one of the three underpasses that the aircraft's fiery fuselage shot through after the crash.
At least three persons in cars struck by the burning plane died in the crash, which also killed 154 passengers. One person survived the crash, 4-year-old Cecilia Cichan. Rescuers found the burned and crying child under the body of a woman, presumably her mother, who perished in the crash. The girl's condition was upgraded Tuesday from critical to serious.
Several other persons on the ground were also injured.
Twenty-five of the victims were employees of General Motors, which operates a testing grounds in Phoenix, the flight's next destination before it was to terminate at John Wayne Airport.
Wayne County Medical Examiner Werner Spitz said that because some remains were charred and fragmented, the death toll could still grow.
Meanwhile, FAA records showed that the plane that crashed, identified by Northwest as "ship 9309," had engine failures on takeoff twice in 1986 and once in 1985, and that as recently as last January it was forced to return to the airport in Memphis, Tenn., after takeoff because of low oil pressure.
Two of the incidents involved turbine blade failures, and the problem engines were replaced, according to a spokesman for Northwest Airlines.
Monday, National Transportation Safety Board member John Lauber, who is heading the Detroit investigation, said there was no physical evidence of an uncontained engine failure, although he left open the possibility of an internal engine problem.
FAA records show the plane was forced to return to Minneapolis 18 minutes after takeoff when the left engine failed in November, 1985. The plane was forced to return to Minneapolis again after takeoff in January, 1986, on one engine, according to Northwest records. Five months later, in April, 1986, the plane landed in San Francisco after a turbine blade broke in an engine.
Northwest Airlines spokesman Bob Gibbons said that at the time of the crash Sunday the plane was equipped with a right engine installed on April 3, 1986, and a left engine installed on Oct. 9, 1986. Neither of the engines on the plane at the time of the crash was involved in the earlier incidents.
Ed Cowles, a spokesman for Pratt & Whitney, manufacturer of the JT8D 200-series engines that were on the Northwest plane and that are used on 408 other MD-80 jetliners, defended the engines, saying they have had "an outstanding safety record."