When two hijacked planes hit the twin towers of the World Trade Center on September 11, 2001, those caught above the point of impact appeared almost certain as doomed to die, especially anyone fatefully trapped in the North Tower.

Yet some people in the highest reaches of the South Tower made it out. For many, their journey down the last intact stairwell was fraught with unfathomable danger and nightmarish terror.

One man who escaped was Joe Dittmar, a father-of-four at the top of the South Tower on a morning when Al Qaeda launched their attack in dreamy blue New York skies.

He says his incredible escape, 20 years ago, still feels like yesterday. Here is his story.