Columbia Investigators Zeroing in on Working Theory of Shuttle Accident

HOUSTON April 23

After nearly three months of sifting through debris and analyzing data, investigators examining the Columbia accident are now focusing their efforts on picking a working theory on what caused the shuttle to disintegrate during re-entry.
Evidence continues to mount that a 2-pound chunk of insulating foam from the shuttle's external fuel tank ripped away during its Jan. 16 launch and hit a seal on the left wing. That would have created a slit large enough to let in hot atmospheric gases as the spacecraft re-entered the atmosphere on its return home two weeks later.
"For 11 weeks we have been saying we don't have any particular scenarios, any favorite scenarios," Harold Gehman Jr., a retired Navy admiral heading the investigation board, said Tuesday during the group's weekly news conference. "I think 11 weeks into this, it's time that we attempted to see where the evidence was pointing us."
Gehman said the board will meet with NASA investigators and officials Thursday to begin the process of trying to come up with a working scenario of what happened. Columbia broke apart over Texas on Feb. 1 as it aimed for a Florida landing. All seven astronauts aboard were killed.
A public hearing was scheduled for Wednesday.
On Tuesday, board members said tests show that a mystery object that floated away from the shuttle while in orbit was likely a so-called T-seal. It's still unclear whether all or part of it drifted off.
The seals are made of reinforced carbon composite and fit between pairs of panels made of the same material that are designed to withstand temperatures of up to 3,000 degrees during re-entry. These seals and panels wrap around the leading edge of each wing.
Navy Rear Adm. Stephen Turcotte, a board member, said he believes some sort of "blunt-force trauma" and not simply wear-and-tear caused the seal to come off.
Physicist James Hallock, a board member in charge of the Transportation Department's aviation safety division, theorized that the hole created by the missing seal got bigger as hot atmospheric gases chipped or broke away at adjoining wing panels.
Testing of a fuel tank similar to the one that propelled Columbia shows at least 74 defects in the insulating foam, many of which are air pockets. Engineers also discovered faulty bonding between some of the layers of foam.
Steven Wallace, a board member and the director of accident investigations for the Federal Aviation Administration, said he and his colleagues also have discovered that seven of the 77 flight controllers involved in Columbia's doomed flight were lacking some of the necessary certifications.
That did not contribute to the accident in any way, but the board still considers it a discrepancy that needs to be addressed, Wallace said.
The board's final report is not expected until midsummer.
"We're beginning a kind of a new phase in the board's work. We're beginning to concentrate on the report," Gehman said. "In the month of May, we'll spend more time deliberating and less time investigating."
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