Whoever conducted the attack, which I believe was Usama and company, didn’t use something other than the airplanes. For your edification, steel weakens at somewhere around 1700 degrees Fahrenheit. Jet fuel burns at over 2000 degrees Fahrenheit. From an engineering stand point there is no argument. You might like to know that steel structures everywhere are protected from fire with sprayed on insulation for this very reason. Any normal building fire is hot enough to collapse a steel structure and requires protection.