Anyway,
My drawn out point was this. Cross reference the specs of the 707 and 767-200:
767-200ER
Maximum Fuel Capacity 23,980 gal (90,770 l)
Maximum Takeoff Weight 395,000 lb (179,170 kg)
Typical Cruise Speed
at 35,000 feet Mach 0.80
530 mph (850 kph)
Basic Dimensions
Wing Span = 156 ft 1 in (47.6 m)
Overall Length = 159 ft 2 in (48.5 m)
Tail Height = 52 ft (15.8 m)
Interior Cabin Width = 15 ft 6 in (4.7 m)
Advanced 707-320B
Wingspan 145 feet 9 inches (44.42 m)
Length 152 feet 11 inches (46.6 m)
Wing Area 3,010 square feet (280 m2)
Gross Weight 336,000 pounds (152,400 kg)
Cruising Speed 607 mph (977 km/h)
The sizes are similar. The 767-200 (fully fueled) gross take off weight is about 18% more than that of the 707.
The point. The hijacked 767's were only on intradomestic routes meaning airlines don’t fully fuel airliners on short hops to minimize fuel consumption. Its estimated the 767's had around 10,000 gallons of jet fuel when they struck the WTC.
Because jet fuel weighs 6.4 lbs per gallon and the 767's empty weight is 180,00 lbs, the 767's that struck the WTC had a gross weight at the time of impact around 244,000 lbs.
That 767 weight is 27% less than the fully fueled gross weight of a 707 carrying over twice! the amount of combustible liquid.
So if the WTC engineers designed the towers to withstand an impact of a fully fueled 707, why did they collapse?
Obviously it has everything to do with the parameters they used when establishing the conditions surrounding a 707 impact, speed, weight, fuel capacity, ect.
But one would imagine, or would at least logically assume they computed tower structure design to withstand the impact from a near fully fueled 707. But only the designers know. Apparently, the blue prints to WTC have been sealed off to the public.
Would make an interesting investigation anyway.