Federal investigators indicated Tuesday that a weather phenomenon known as wind shear may have contributed to the fatal crash of Northwest Airlines Flight 255.
John Lauber, the National Transportation Safety Board member who is heading the inquiry, said that alerting systems at Detroit's Metropolitan Airport sounded several warnings of wind-shear conditions 20 to 30 minutes before the crash.
These warnings were included in recorded weather information that pilots routinely monitor before takeoff. The advice is general in nature, and what weight to give it is up to the pilot.
The warnings raise the possibility that the plane, ultimately headed for Orange County's John Wayne Airport, may have encountered a sudden wind-shear downdraft that deprived the aircraft of the lift it needed to take off.
The wind-shear advisories were broadcast for planes taking off from an 8,500-foot runway in a southwesterly direction, but shifts in wind direction prompted controllers to reverse the direction in which the planes took off about 15 to 20 minutes before the takeoff of Flight 255. There were no further wind-shear alerts after the reversal of the runway direction.
However, the NTSB disclosed that preliminary studies of the "black box" cockpit voice recorder showed that the pilot and co-pilot discussed the weather before takeoff.
Lauber said they talked of "something out there" and said they would not want to have to make a left turn into it after takeoff. The plane was cleared for a right turn.
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. 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.
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 microburst 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 downdrafts 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 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.
Lauber told reporters Tuesday night that a cockpit crew of another plane waiting to take off watched Flight 255 as it lifted off the runway and concluded that the liftoff angle was "too steep.'
Aviation officials said the jetliner was very heavy on takeoff, but NTSB officials said its weight apparently was within regulations.
Northwest spokesman Robert Gibbons said the plane was crowded but not dangerously so. "There wasn't room for another adult on that aircraft," he said. "But that's how many planes fly."
On Monday, reports by some observers that the plane's left engine was on fire as it took off had caused attention to be focused on the possibility that engine failure was a major contributing factor in the disaster. Investigators continued to examine that possibility.
A Federal Aviation Administration source said that flames coming from the engine baffles can sometimes create the false impression that an engine is on fire.
Lauber said that maintenance records for both engines for the last 90 days had been studied by NTSB technicians Tuesday and they "characterized it as a pretty healthy airplane . . . all required maintenance was complied with."
Engines Stay at Site
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.
"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."
At Tuesday night's briefing, Lauber conceded that there was still some confusion about the death toll in the crash and said he was not certain where the discrepancies lay. He said some of the passengers may have traded tickets acquired under so-called "frequent flier" programs and thus may not have been flying under their own names.
Lauber said that the latest NTSB figures indicated that there were 153 victims aboard the plane and one victim on the ground, but some estimates have run as high as a total death toll of 157.
"I know this is difficult, but I hope the conflicts will be resolved soon," Lauber said.
Wayne County Medical Examiner Werner Spitz said that because some remains were charred and fragmented, the death toll could still grow.
Twenty-five of the victims were employees of General Motors, which operates a testing ground in Phoenix, the flight's next destination before it was to terminate at John Wayne Airport.
In Mission Viejo, neighbors of the Reid Bushong family said Tuesday that they had been told that Rhett Bushong, 19, of Mission Viejo, had died in the crash. Bushong had been attending a family reunion in Toledo, Ohio, with his parents. He was returning ahead of them in order to attend the opening of football practice Monday at Saddleback College. He was transferred onto the Northwest flight Sunday because his scheduled flight was late.
One person aboard the airliner 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.
Previous Engine Failures
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.
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.
Gibbons, the airline spokesman, 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."
Lauber said Tuesday night that the cockpit voice recorder indicated that, moments after liftoff, an automatic stall warning device aboard the aircraft announced in a computerized voice: "Stall! Stall!" Lauber said the warning continued for "some period of time." Then came the "sounds of impact, the plane breaking up."
He said that he could not characterize the warning as extraordinary. "I can't characterize it at all," he said.
Authorities said Flight 255's captain, John R. Maus, 57, of Las Vegas, was also qualified to fly the DC-3, DC-9, Boeing 727, 757 and 767. They said FAA records show that he had no record of violations or accidents.
As the federal investigators sought the cause of the crash, Wayne County sheriff's officials struggled to identify the bodies of the victims. The county medical examiner said some remains may never be identified.