trapping occupants, although one freight car from the lobby to the fortieth floor remained operable. Unlike in the North Tower, where Flight 11 destroyed all three stairwells, in the South Tower one exit route from the uppermost floors remained at least partially intact: Stairwell A. Although located in the central core, Stairwell A was positioned to the west of where Flight 175 entered and was shielded by heavy elevator equipment. That left the stairwell potentially usable for anyone who could reach it. Structurally, the South Tower fared worse than its twin. The plane severed thirty-three
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