"Everything is on the table. We release information as we get it. But that doesn't mean there's any special significance to it," he said.

On Saturday, the board was set to travel to Lockheed Martin Corp.'s facility in Louisiana, where shuttle external tanks are built. The board has already traveled to Kennedy Space Center in Florida and Marshall Space Flight Center in Alabama.

Flight director Leroy Cain, who was on duty Feb. 1 when the shuttle broke apart, also didn't want to place too much emphasis on the breach at this stage in the investigation.

"It's a possibility, along with the whole range of things that are possibilities. But there are many, many other possibilities," Cain said Friday.

Analysis of what could have caused a hole in the shuttle continues. One possibility raised from the very start of the investigation, is that Columbia was damaged by a hard piece of foam insulation that fell off the external fuel tank during liftoff.

George J. Gleghorn, a retired TRW Inc. engineer and former member of the NASA Aerospace Safety Advisory Panel, said he believes the breach probably happened during liftoff.

"I would be surprised if something happened that caused a breach of the skin without being noticed unless it was that incident that happened during the ascent phase," Gleghorn said.

Cain acknowledged Friday he immediately thought of the foam debris right after he was first told of sensors breaking down in the spacecraft's left wing minutes before it came apart over Texas, killing its crew of seven astronauts.

"That gave me pause," Cain said. But he also said when he learned about the sensor readings, he did not imagine it would spell the end for the shuttle and its crew: "I did not think that we would lose it."

Investigators believe the breach allowed a stream of superheated gases to penetrate the shuttle's left wing, starting a cascade of failures.

One by one, sensors in Columbia's left wing recorded unusual readings as the shuttle approached the California coast. The precise meaning of those readings was not immediately clear to Mission Control, Cain said.

The wings have only a few sensors, not enough to indicate if the landing gear hatch had come open or had been breached to allow the superheated gases, called plasma, to penetrate the wing, he added.

Most ominous of the readings was a spike in temperature in the compartment containing Columbia's left landing gear that suggests gases 2,000 degrees or hotter had infiltrated the shuttle.

To do so, they would have had to bypass the layer of tiles and other insulating material designed to protect the spacecraft from the searing heat of re-entry. The investigation board has said missing tile would not have allowed heat to simply radiate into the interior of the wing and cause the rise in temperature.

Cain said Friday he doesn't believe his flight team could have done anything different to prevent the disaster.

Gehman said he will add one or two authorities in high-altitude aerodynamics and thermal engineering to the nine-member board to bring more expertise to the investigation. The board will also conduct some key tests independently of NASA, but not double-check everything the agency does, he said.

The board has been criticized by members of Congress and others as not being sufficiently independent of NASA.

Search crews continued to comb Texas and Louisiana for more debris from Columbia. On Saturday, teams were to search an area of the Sandia Mountains near Albuquerque, N.M. So far, no debris has been found west of Fort Worth, Texas.