The tail section of American Airlines Flight 587 jerked the plane from side to side at least three times before it crashed into a New York City suburb Nov. 12, a National Transportation Safety Board report released yesterday indicates.
Investigators made no conclusions on what caused the lateral movements. “The NTSB continues to investigate the cause of the rudder movements,” said the report, which was based on flight-data recorder information.
The agency said again yesterday there was no evidence of a terrorist attack or sabotage in the crash that killed 265 persons. The tail fin and rudder sheared off the Airbus A300-600 after the airplane hit turbulence created by the wake of a Japan Air Lines 747. That plane had taken off less than two minutes earlier from New York’s John F. Kennedy International Airport.
The NTSB said Monday that the turbulence was not great enough by itself to explain why the tail section broke off and Flight 587 crashed.
“Turbulence is significant,” said John Clark, the NTSB’s aviation-safety director. “It’s a player. But we don’t see a huge vortex that just came along and knocked the tail off.”
Passengers inside the airplane would have felt only a slight side to side movement as Flight 587 hit the two vortexes of turbulence from the Japan Air Lines flight, according to the NTSB report. But then suddenly, the airplane made three abrupt jerks for reasons that remain unexplained.
“During the last eight seconds of [flight-data recorder] data, the plane experienced three stronger lateral movements. These lateral forces corresponded in time with rudder movements.”
As the airplane apparently started breaking apart in flight, the recorded data became harder to analyze.
“The [flight-data recorders] rudder data become unreliable about 2.5 seconds before the end of the recording, and sound-spectrum analysis shows that engine sounds can be heard on the cockpit voice recorder beyond that point,” the NTSB report said.
The airplane was in the air only 103 seconds from liftoff to impact, the report said. It also ruled out the possibility of an engine explosion, which some witnesses reported initially.
Another possibility being investigated is that composite materials used to manufacture the tail section were weakened from a 1994 bout with turbulence and finally snapped during the Japan Air plane’s turbulence.
The Federal Aviation Administration has ordered inspections of the tail assembly of the French-built A300-600s and the A-310s, both of which are made with nonmetallic composite materials. American Airlines already inspected its 34 A-300 series planes and found no defects.
Boeing Co. spokeswoman Mary Jean Olsen said the composite materials her company uses on the tail section of its Boeing 777 are “stronger and more flexible than metal.”
She also said composites used by airplane manufacturers are similar. The biggest differences between the airplanes are the manufacturers themselves, she said.
“The design features are different between different manufacturers,” Miss Olsen said.