The more I think about what has been said and what my first reaction was. Consider this —— Perhaps it was a dirigible (think the Goodyear Blimp) taking shots of the completion of the Twin Towers. They look fairly new in this shot. Maybe the purpose of the photo is to show the completion of the Trade Center.
No outside walkways, especially not heavy ship-like steel as shown in the pic, on any of the blimps in use in the USA.