The scene in mission control as contact with the shuttle is lost. Photo: Spaceflight Now/NASA TV.

In the final minutes of shuttle Columbia's doomed reentry, flight controllers began to see indications of a major problem in the area of the shuttle's left wing, NASA officials said on Saturday in their first detailed news briefing since the tragedy.

Just prior to the shuttle's break-up, a series of sensors in the wing failed one by one, as though their wires had been cut, shuttle program manager Ron Dittemore said.

"I have to caution you that we cannot yet say what caused the loss of Columbia," he said. "It's still very early in our investigation and its going to take us some time to work through the evidence, the anaylsis and clearly understand what the cause was."

Sensors recording temperatures in the hydraulic systems on the inboard and outboard elevons were the first to go offline at about 8:53 a.m. EST (1353 GMT), chief flight director Milt Heflin said. About three minutes later, increased temperatures were noted in the compartment housing the left main landing gear.

Around 8:58 a.m. EST (1358 GMT) three bondline temperature sensors in the left wing, embedded in the structure of the vehicle, suddenly stopped working. Then at around 8:59 a.m. EST (1359 GMT), the temperature and pressure sensors for both tires on the left main landing gear dropped offline. A total of eight measurements were lost.

Throughout this time the shuttle continued to fly as planned, streaking through the upper atmosphere at just over 18 times the speed of sound.

Chief flight director Milt Heflin explains the sequence of events. Photo: Spaceflight Now/NASA TV.

"We saw nothing else to indicate any difficulty at all," Heflin said.

The loss of one of these final measurements did trigger a warning in the cockpit, providing the crew with perhaps their first clue something was going very wrong.

"The measurement was no longer reading -- it was not giving an indication. It's as if someone just cut the wire," Dittemore said.

The astronauts were acknowledging this alarm when voice communications with the shuttle abruptly lost. The orbiter was at an altitude of 207,135 feet.

"During this time we lost the data and that's when we clearly began to know that we had a bad day," Heflin said.

The orbiter's left wing had been struck by a piece of foam that broke away from the fuel tank during shuttle's climb to orbit on January 16. NASA engineers had determined that the impact had not caused any serious damage.

Shuttle program manager Ron Dittemore discusses the launch incident. Photo: Spaceflight Now/NASA TV.

In the wake of Saturday's tragedy, Dittemore said "we can't discount that there might be a connection, but we have to caution you and ourselves that we can't rush to judgement on it. There are a lot of things in this business that look like the smoking gun but turn out not even to be close."

The foam was seen breaking free from the bi-pod area where the orbiter nose attaches to the tank. The event is marked by a white puff between the wing and tank and is visible in launch video.

Dittemore said foam was also shed from the same area of the external tank on STS-112 -- two flights ago in October. None of the foam appeared to break loose during a November mission.

Prior to Saturday's tragedy, a review was being conducted to understand why two of the last three missions had suffered from the problem. The inquiry was to have been completed before the next shuttle was cleared for flight.