By the time it broke up the shuttle was spinning out of control

Analysis of the last two seconds of data transmitted by the shuttle as it plummeted to Earth shows that a command was sent to disengage the autopilot.

But US space agency (Nasa) officials investigating the loss of the orbiter, which broke up on 1 February killing all seven of its crew, say the action could have been accidental, or considering the garbled nature of the data, may not have even happened.

The vehicle was spinning out of control at the time.

Shuttle instruments indicated a slow pirouette of 20 degrees per second, or a revolution every 18 seconds - but since this is the maximum speed the sensors could register, the rate of spin may in fact have been much higher.

Crucial 32 seconds

A breach in the left wing, which allowed hot gases to penetrate, is thought to have triggered the disaster.

Nasa experts are combing the data the shuttle transmitted in the final 32 seconds of flight, attempting to recreate the events of its failed re-entry moment by moment.

They can't ensure the integrity of any of the data, and some of the stuff that they are saying may be inaccurate or misinterpreted Nasa official

Following the last spoken word transmission with Columbia, in which Commander Rick Husband conversed with a ground controller in Houston, the shuttle sent a further five seconds of data. Then there was silence for 25 seconds, followed by a final two-second burst of data just before all communication was lost.

The information concerning the autopilot was gleaned from that final two second spurt, which the shuttle transmitted at about 0900 (1500 GMT).

Beyond help

Citing "sources working with investigators" ABC news reported on Sunday that data "indicates that one of the pilots... may have attempted to disengage the autopilot in what would have been a futile effort to regain control of Columbia".

During re-entry the shuttle flies on autopilot until it has reduced its velocity to below the speed of sound, but the pilots on board are trained to carry out a full manual re-entry in the event of an emergency.

Retrieved data could yield further clues

Manually moving the steering control or "stick" on the shuttle automatically cuts off the autopilot - something easily done by accident.

Even before Columbia began experiencing problems, Husband reported that one of the crew knocked the "stick" by accident, causing the autopilot to briefly disengage - an error that was swiftly rectified.

Nasa officials have stressed that the override attempt may not even have happened.

"The data are really suspect. They can't ensure the integrity of any of the data, and some of the stuff that they are saying may be inaccurate or misinterpreted," one official told Associated Press.

Determining whether such an action could have been intentional is made all the more difficult by the fact that the shuttle stopped transmitting data, making it impossible to tell whether the autopilot did actually disengage.

But one thing Nasa's investigators do seem agreed on is that nothing any of the seven astronauts on board attempted could have saved the stricken shuttle.