Re: Tonight there was a documentary on just why the towers collapsed. It appears that the structural engineer did allow for the impact of an aircraft, but not for the heat that would be generated by the nearly full fuel load on a passenger jet

That sounds like the Nova (a US PBS show) broadcast that was presented earlier this year, along with a written report on what happened.

the same Nova show is being rebroadcast this coming week (in NY on WNET/13 on Tuesday Sept. 10) you can check the pbs web page (PBS.Org) for local listing and broadcast times.

it did an excellent analysis of why the tower fell. the same inovative engineering that provide wide open floor plans contributed to the floors failures.