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NTSB narrows investigation of Flight 587 crash

WASHINGTON (CNN) -- With no evidence of sabotage, investigators are focusing on two rudder components and the electronic controls of an American Airlines jet that plunged from the sky and crashed into a New York City neighborhood last month, the head of the National Transportation Safety Board said Wednesday.

"We're looking to see if there was a problem with the electronic controls, with the computer controls themselves," said Marion Blakey, chairman of the safety board, adding that the plane's maintenance records appeared "very normal" but are still being scrutinized. "We have to determine whether this was a mechanical problem or something more subtle. We don't know. And we don't know of course whether it contributed to the crash or not."

Blakey said that on the morning that Flight 587 departed from New York's John F. Kennedy International Airport, the pitch trim control "was found to be inactive" and needed to be reset. That device, she said, controls "some of the subtle movements of the rudder that keep the planes stable in flight." The yaw damper also initially failed the pre-flight check, but it too was reset by a mechanic and the problem was reported resolved, according to the NTSB.

An aviation safety expert said the NTSB will probably take a much closer look at the components, which control the slight side-to-side movements a plane makes during flight and allow the aircraft to fly straight comfortably.

"If the yaw damper fails, this has the potential of pushing the rudder further than the pilots intended it to go, which could cause control problems," explained aviation expert Jim McKenna.

Flight data recorder information from Flight 587, which crashed soon after takeoff, shows the plane experienced violent side-to-side movements coinciding with movements of the rudder only seconds before the plane went out of control and plunged into a Queens neighborhood November 12, killing 260 people aboard and five on the ground.

Investigators say the tail and rudder section, followed by the engines, fell off before the plane hit the ground.

"Investigators are going to want to get a good handle on how effective the reset (of that yaw damper) was," McKenna said. "They need to make sure the reset is valid and didn't just have the appearance of fixing the problem."

No evidence of sabotage

Blakey cautioned that it was too early to conclude the cause of the accident, but she stressed that it appeared to be just that -- an accident.

"We have not seen any evidence of criminal activity, any evidence of sabotage, any evidence that points to a bad actor," she said. "Everything points to an accident."

As part of the investigation, the NTSB said a team of investigators flew to Toulouse, France, to work with counterparts at Airbus Industrie and the French Accident Investigation bureau to "familiarize themselves with the operation of the A300-600 rudder system, including a detailed examination of the rudder travel limiting systems installed on the plane."

The NTSB said Airbus is providing a systems simulator "to assist the investigation in simulating possible malfunction scenarios within the rudder system of the aircraft."

In addition, investigators are working with their European counterparts to study how aerodynamic loads, such as wind or wake turbulence, affect the composite components of the vertical stabilizer or tail fin section of A300 Airbus aircraft like the one that crashed in New York.

Airbus said the Airbus A300-600 is the first generation of planes it manufactured that include tail sections made up of a new kind of composite material constructed of graphite and resin.

Investigators confirmed that inspections in New York show that the six primary attachment points made of metal that connect the vertical stabilizer with the rest of the plane were found still attached and in their proper position. That has led investigators to focus more closely on whether microscopic defects or wear-and-tear of the composite components housed inside the attachment points and vertical stabilizer caused the rudder to shear off.

The tail section, including the vertical stabilizer (tail fin) and rudder, have been delivered to NASA Langley Research Center in Hampton, Virginia, to undergo nondestructive inspections -- like ultrasound, thermography, and tap testing -- to test the composite components.

NTSB investigators also said both engines were transported to an American Airlines facility in Tulsa, Oklahoma, where an "engine teardown" -- a detailed examination -- was conducted. According to the NTSB, "there was no evidence found of an uncontained engine failure, case rupture, in-flight fire, foreign object damage such as a bird strike, or pre-impact malfunction."

Tests performed on the auxiliary power unit of the engine also showed no evidence of any rotational damage to the compressor impellers or rotors or any evidence of in-flight fire, case rupture, uncontainment or hot air leak.


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