Engineer details Echelon damage

AUSTIN (KXAN) - The final structural engineering report on the Echelon building in North Austin shows how close a plane came to flying completely through the building in February 2010.

The report, prepared by Structures , said the plane, flown by Joseph Stack, impacted the building at the second floor line, which caused it to stop immediately and fall down outside the building instead of going through the second floor, which likely saved dozens of lives.

Stack was angry with the government and had a grudge against the IRS, which had offices in the Echelon building at the time.

"If the plane hit a little bit higher, it could have gone right into the building and could have killed a lot more people," said engineer Shane Tanner. "A lot more people."

Tanner prepared the report for Structures and said the luck of the impact was just a matter of inches.

"He was aiming for windows, really- and so he just hit at the perfect spot to just stop it, really," said Tanner. "It could have hit the column and knocked the column out and could have brought the whole building down."

According to the report, Stack's plane impacted the building at the equivalent of nearly 1.2 million pounds of force and caused the entire building to sway 4 inches and then back 3 inches. The impact also took out the building's water line which prevented the sprinklers from coming on to put out the fire. Stack had loaded his plane with extra fuel and the fire spread quickly and did most of the damage to the building.

"It was amazing to see that a structure can actually resist that much of an impact without catastrophic failure," said Tanner.

Stack died in the crash which also killed IRS employee Vernon Hunter , who was working inside the building.