Leonardo starts writing on a flying machine and comparing it with the notes he has already taken on the flight of birds. He states that "the bird" (machine) must attain a high altitude it case it were to turn over so as to have enough time to right itself. He notes that the framework needs to be strong with leather laces and raw silk for the ribs. He also adds that there should not be any metal in the machine because of its tendency to wear or break under stress.