"Collapse: How the Towers Fell."
According to the show's experts, although jet fuel might optimally
reach temperatures approaching 2000deg F, fully one-half of [ Flight 11's]
fuel burned outside of the tower.
consistent with sources which state that each aircraft was carrying about
10,000 gallons of fuel , and with FEMA’s estimate that about 4000
gallons of fuel burned within each tower. 
remaining half, which ignited inside the tower, burned up in about eight
minutes. And that analysis was based on the first crash (8:46 am), into the
North tower. As can be clearly seen in video footage, a much higher
percentage of the fuel burned outside the South Tower, in the second crash
9 notes that at 9:03 flight 175 hit the South tower, crashing thru the 77th
to 85th floors. “The plane Banked as it hit…, leaving portions of the
building undamaged on impact floors. As a consequence--and in contrast
to—the…North Tower, stairwell A initially remained passable from at least the
91st floor down, and likely from top to bottom.”