Twin Terrors

PLANES SLAM TOWERS...

8:45 a.m. American Airlines Flight 11, a Boeing 767 hijacked en route from Boston to Los Angeles with 92 passengers aboard, slams into the north tower

9:06 a.m. United Airlines Flight 175, also a Boeing 767 hijacked en route from Boston to Los Angeles with 65 passengers aboard, banks hard and slices through the south tower

...AND WEAKENED BUILDINGS COLLAPSE

10:00 a.m. The sudden collapse of the south tower traps hundreds of rescuers below, in addition to perhaps thousands of workers in the building. Debris guts the 4 World Trade Center building below

10:29 a.m. Weakened by its imploded twin, the north tower collapses, raining more debris and crushing buildings and rescuers below

5:25 p.m. As fires and debris finally take their toll, the 7 World Trade Center building falls

FIRST IMPACT American Flight 11

1 World Trade Center Second to collapse Completed: 1970 Height: 110 floors Floor Sizes: (9-105) 45,000-50,000 sq. ft. Elevators: 97 passenger, 6 freight

WHO WAS INSIDE The Port Authority of New York and New Jersey leased six floors of the north tower. Cantor Fitzgerald Securities, on floors 101-105, cannot account for 1,000 of its employees

SECOND IMPACT United Flight 175

2 World Trade Center First to collapse Completed: 1972 Height: 110 floors Floor Sizes: (2-109) 45,000-50,000 sq. ft. Elevators: 97 passenger, 6 freight

WHO WAS INSIDE Morgan Stanley Dean Witter was the single largest tenant in the south tower, leasing 21 floors. Both buildings hold 50,000 people

The 360-ft. television mast on Tower 1 supported 10 television antennas and numerous other services. Ten television stations, including all the major networks, broadcast from the mast

7 World Trade Center Third to collapse

All lower building around the towers virtually destroyed by falling debris

WHY DID THEY COLLAPSE?

Each of the towers, more than 200 ft. wide on each side, contained a central steel core surrounded by open office space. Eighteen-inch steel tubes ran vertically along the outside, providing much of the support for the building

Once the plane damaged the central core, the weight was redistributed to the outer steel tubes, which were slowly deformed by the added weight and the heat of the fires

Sources: Port Authority of New York and New Jersey; Associated Press; Skyscrapers, by Judith Dupre, Perpetual Motion, by Joe Mysak and Schiffer