Audio files reveal 9/11 air horror

Newly posted audio files depict the horror of 9/11 unfolding in the sky as air traffic controllers struggled to follow the faint tracks of hijacked planes, fighter jets tried in vain to chase them down and a flight attendant made a desperate appeal for help.

The sound files add a layer of emotion to previously published transcripts, as puzzlement and frustration seeps into the voices of controllers, military commanders and even pilots watching the attacks from the sky.