Second plane to hit World Trade Centre was travelling faster
Researchers believe the second hijacked plane to hit the World Trade Centre tower was travelling about 100 mph faster than the first.
Investigators are focusing on the speed of the two planes as they seek to explain what caused the south tower to collapse first, even though it was hit later, said reports.
Researchers have closely studied videos, sound recordings and radar to estimate how fast the two jetliners were moving.
Studies show that both planes were travelling well over the federal limits for altitudes below 10,000 feet.
The second plane was flying so fast that it was in danger of breaking up in the air as it approached the south tower, Boeing spokeswoman Liz Verdier said.
"These guys exceeded even the emergency dive speed," Verdier said. "It's off the chart."
Two studies have analysed the speed of the planes, one by the Federal Aviation Administration in consultation with the National Transportation Safety Board and the other by Massachusetts Institute of Technology.
The government's calculations put the speed of the first plane at 494 mph and the second at 586 mph.The MIT analysis determined the first plane was travelling 429 mph, and the second 537 mph.
The south tower collapsed 56 minutes after the crash. The north tower stood for 102 minutes.
Structural engineers have not determined to what extent the speed of the planes affected how long the buildings stood. They are studying many factors, including the point at which each tower was hit.
