"We're going to do something," Thomas Burnett told his wife. Todd Beamer said: "Let's roll." And then, it was believed, they fought their way to the cockpit using a food trolley as a shield, seized the controls and forced the plane to crash into a Pennsylvania field rather than allow it to reach the White House.

Now, however, US investigators, citing cockpit recordings which remain secret, are changing the story of the crash which claimed the lives of 33 passengers, seven crew members and four terrorists.

The FBI director, Robert Mueller, told congressional investigators in a closed briefing last year that the terrorist pilot Ziad Jarrah had decided to crash the jet himself because of the passenger insurgency.

The FBI maintains that its finding, disclosed in a passage buried in a 858-page report, does not diminish the passengers' heroism: "While no one will ever know exactly what transpired in the final minutes of Flight 93, every shred of evidence indicates this plane crashed because of the heroic actions of the passengers."

Those who have heard the recording describe it as virtually indecipherable. Nonetheless, some passengers' families who heard it and received the FBI's best attempt at a transcript dispute the bureau's claim. Burnett's wife Deena said a hijacker tells Jarrah in Arabic to crash the plane, but Jarrah refuses.

Towards the end of the tape the sound of breaking glass and crockery lends credence to the theory that passengers rushed the aisle with the food trolley.

"It is totally obvious listening to that flight recorder that they made it into the cockpit," Mrs Burnett said. "You cannot listen to the tape and understand it any other way."