Were The Twin Towers Designed To Survive The Impact Of The Airplanes?

Both technical calculations and testimony from WTC structural engineers confirm that the Twin Towers were built to withstand the impact from the passenger jets that hit them on 9/11.

Airplane impact tests conducted by WTC structural engineers during the design of the Twin Towers used the Boeing 707, which was one of the largest passenger jets in the world at the time. The results of the test, carried out early in 1964, calculated that the towers would handle the impact of a 707 traveling at 600 mph without collapsing.

Even though the two Boeing 767 aircraft that were said to be used in the 9/11 attacks were slightly larger than the 707, technical comparisons show that the 707 has more destructive force at cruising speed. The following analysis was compiled by 911research.net:

The maximum takeoff weight for a Boeing 707-320B is 336,000 pounds.
The maximum takeoff weight for a Boeing 767-200ER is 395,000 pounds.

The wingspan of a Boeing 707 is 146 feet.
The wingspan of a Boeing 767 is 156 feet.

The length of a Boeing 707 is 153 feet.
The length of a Boeing 767 is 159 feet.

The Boeing 707 could carry 23,000 gallons of fuel.
The Boeing 767 could carry 23,980 gallons of fuel.

The cruise speed of a Boeing 707 is 607 mph = 890 ft/s,
The cruise speed of a Boeing 767 is 530 mph = 777 ft/s.

So, the Boeing 707 and 767 are very similar aircraft, with the main differences being that the 767 is slightly heavier and the 707 is faster.

In designing the towers to withstand the impact of a Boeing 707, the designers would have assumed that the aircraft was operated normally. So they would have assumed that the aircraft was traveling at its cruise speed (i.e., not at faster speeds perhaps flown by suicide pilots). With this in mind, we can calculate the energy that the plane would impart to the towers in any accidental collision.

The kinetic energy released by the impact of a Boeing 707 at cruise speed is
= 0.5 x 336,000 x (890)^2/32.174
= 4.136 billion ft lbs force (5,607,720 Kilojoules).

The kinetic energy released by the impact of a Boeing 767 at cruise speed is
= 0.5 x 395,000 x (777)^2/32.174
= 3.706 billion ft lbs force (5,024,650 Kilojoules).

From this, we see that under normal flying conditions, a Boeing 707 would smash into the WTC with about 10 percent more energy than would the slightly heavier Boeing 767. That is, under normal flying conditions, a Boeing 707 would do more damage than a Boeing 767.

So what can be said about the actual impacts?