Yes the analysis took the B 25 Empire State Building crash as a model and assumed a 707 lost in bad visibility at mandated 200 kt max airspeed for operations below 10 000 ft as the NYT reference notes page 13 It appears from the article now that I re read it that somebody at Yamasaki or Emery Roth s offices heard a garbled version The article also points out on the following page that nobody considered the fire as Zdawg notes there s no discussion of why though I suspect my theory is close to the mark Studies of that kind are expensive and if Robertson wanted to do the structural calcs on his own dime that didn t mean that the owner or architect would ante up for a full study of an airplane induced fire talk