[Xist]

Why wasn’t the hole as wide as a 757’s nearly 125-foot wingspan? A crashing jet doesn’t punch a cartoon-like outline of itself into a reinforced concrete building, says ASCE team member Mete Sozen, a professor of structural engineering at Purdue University.

Some windows near the impact area did indeed survive the crash. But that’s what the windows were supposed to do—they’re blast-resistant.

Conspiracy theorists insist there was no plane wreckage at the Pentagon. [...] Blast expert Allyn E. Kilsheimer was the first structural engineer to arrive at the Pentagon after the crash and helped coordinate the emergency response. “It was absolutely a plane, and I’ll tell you why,” says Kilsheimer, CEO of KCE Structural Engineers PC in Washington, D.C. “I saw the marks of the plane wing on the face of the building. I picked up parts of the plane with the airline markings on them. I held in my hand the tail section of the plane, and I found the black box.” Kilsheimer’s eyewitness account is backed up by photos of plane wreckage inside and outside the building. Kilsheimer adds: “I held parts of uniforms from crew members in my hands, including body parts. Okay?”

Popular Mechanics: Myths About the 9/11 Pentagon Plane Crash: Debunked

The pentagon was made with close-set concrete columns with spiral rebar, which maintained integrity for long enough for most employees to escape:
History.com: How the Pentagon's Design Saved Lives on September 11