The NTSB said it was trying to determine which problem happened first and caused the other.
The NTSB forwarded the analysis to the NYPD, which is leading the investigation, a spokesman said.
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According to the NTSB, the incident was the largest oil spill in the Midwestern United States.
One NTSB member voted against the proposed safety alert, saying it diminished other alerts.
The NTSB investigated and found an independent contractor was to blame for rupturing the line.
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"I don't believe most state lawmakers would say (the NTSB recommendation) is viable, " Adkins said.
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The National Transportation Safety Board (NTSB) is investigating the incident in Boston on 7 January.
One of the factors the NTSB will examine is the crash-worthiness of the cars.
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The NTSB report released Friday finalizes preliminary conclusions described in another report released in December.
"This accident hits especially close to home, with the involvement of an NTSB employee, " Hersman said.
An NTSB investigator will serve as a U.S. liaison to Canadian investigators, authorities said.
Investigating that incident, the US National Transportation Safety Board (NTSB) said the battery did not overcharge.
"It was an amazing piece of airmanship, " said Peter Goelz, a former NTSB managing director.
The NTSB is the nation's independent accident investigation board, while FAA regulates aviation safety.
In addition to the NTSB investigation, Japanese and French aviation officials also have launched investigations.
The NTSB recommended race sponsors evaluate the course to minimize potential conflicts with spectators.
The plane did not issue a distress call before losing radar and radio contact, the NTSB said.
The NTSB has allowed Metro-North to begin removing some of the track and wire from the scene.
However, the NTSB has not yet found out what caused the short circuit in the first place.
The NTSB said that toxicology tests of the flight crew were negative for alcohol or illicit substances.
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" Another NTSB board member said the proposal's target -- distracted driving -- is "the new DUI.
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The thumps are followed by a "rapid decrease in engine sounds, " said NTSB board member Kitty Higgins.
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Responding to the 2007 NTSB mandate, the FAA drafted similar policies in 2008, but never implemented them.
The department should seize this opportunity to implement NTSB-mandated comprehensive fatigue-management policies in all modes of transportation.
Neither event should have occurred on the Dreamliner, Deborah Hersman, chairwoman of the NTSB, said last week.
The NTSB said that Leeward was likely incapacitated in the very first second of the accident sequence.
The NTSB said Saturday the plane did not issue a distress call before losing radar and radio contact.
Cranes will have to remove the wreckage from the tracks once the NTSB has finished its on-site probe.
The NTSB's brief description of the accident on its website, however, doesn't correspond with on-scene descriptions of weather.
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Townes' testimony came after the NTSB released a dramatic transcript of the last moments of the doomed flight.
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