CAPE CANAVERAL, Fla. (AP) -- NASA engineers settled into their long, joyless task of figuring out how space shuttle Columbia broke apart, saying conditions in the shuttle's final minutes point to a possible problem with its critical heat-protection tiles.

NASA says new evidence shows that the temperature on Columbia's left side shot up and the ship was buffeted by greater wind resistance before it disintegrated over Texas, killing all seven astronauts aboard. Those conditions forced its automatic pilot to quickly change course.

The combination of these events suggests that thermal tiles may have been damaged during launch. The shuttle's exterior is covered with thousands of tiles designed to protect it from the extreme heat of re-entry.

Despite the possible clues, shuttle program manager Ron Dittemore stressed Sunday that the information was only preliminary.

''We've got some more detective work,'' Dittemore said. ''But we're making progress inch by inch.''

NASA Administrator Sean O'Keefe also stressed that other theories couldn't be ruled out yet.

The foam ''is one item of many, many pieces of evidence we're collecting in an effort to try to determine the cause of this accident,'' O'Keefe said Monday on CBS' ''The Early Show.'' ''We're not ruling anything out and that is not a favored theory at this point.''

While engineers at the Johnson Space Center in Houston analyzed billions of bits of electronic data radioed to Earth by Columbia on Saturday morning, state and federal officials collected bits and pieces of the shattered spacecraft over a broad swath of east Texas and Louisiana.

The debris was being catalogued and trucked to an Air Force base in Louisiana. Some human remains also have been recovered from the astronaut crew.

President Bush had arranged a meeting Monday with O'Keefe to get an update on the disaster.

Computer data indicates that moments before Columbia broke apart on Saturday on its way toward a landing in Florida, temperatures rose in the wheel well and on the fuselage on the left side of the shuttle. The abnormal readings were on the same side of the craft that was hit by peeling fuel-tank insulation during the craft's Jan. 16 launch, NASA engineers said.

Dittemore said engineers also were planning to examine 32 seconds of computer data that earlier had been ignored because it was considered flawed. The data came just before all communications with Columbia were lost.

NASA engineers spotted the peeling fuel tank insulation on high speed cameras that recorded the launch of Columbia. Dittemore said the possible effects on the tiles from the insulation were studied aggressively while the shuttle was still aloft, but engineers concluded ''it did not represent a safety concern.''

''As we gather more evidence, certainly the evidence may take us in another direction,'' he said.

NASA's best estimate is the piece of foam was 20 inches at its greatest length, spokesman Allard Beutel said Monday.

Dittemore said engineering data shows a rise of 20 to 30 degrees in the left wheel well about seven minutes before the spacecraft's last radio transmission. There followed a rise of about 60 degrees over five minutes in the left hand side of the fuselage above the wing, he said.

The shuttle temperature rose the normal 15 degrees on the right side over the same period, he said. All the readings came from sensors underneath the thermal tiles, on the aluminum hull of the craft.

The temperature spikes were accompanied by an increased drag, or wind resistance, that forced Columbia's automated flight control system to make rapid adjustments maintain stability. Dittemore said the corrections were the largest ever for a shuttle re-entry, but still within the craft's capability.

Lockheed, the maker of the fuel tank under scrutiny, said Sunday that NASA used an older version of the tank, which the space agency began phasing out in 2000. NASA's preflight press information stated the shuttle was using one of the newer super-lightweight fuel tanks.

Harry Wadsworth, a spokesman for Lockheed, said most shuttle launches use the ''super-lightweight'' tank and the older version is no longer made. Wadsworth said he did not know if there was a difference in how insulation was installed on the two types of tanks.

Wadsworth said the tank used aboard the Columbia mission was manufactured in November 2000 and delivered to NASA the next month. Only one more of the older tanks is left, he said.

Dittemore said the tank, though no longer manufactured, had been used for many years and was between 6,000 and 7,000 pounds heavier than the newer version. ''We had no reason to doubt it capability.''

Earlier Sunday, O'Keefe named a former Navy admiral to oversee an independent review of the accident, and said investigators initially would focus on whether the piece of insulation caused the damage that brought down the shuttle.