(under subclass 6) Aeronautical machines, which may be altered so that the major sustaining agency is either the
aerodynamic action upon airfoils in fixed relation to the machine or the vertical component of thrust developed by screw propellers. This includes machines which are designed to be operated without change, either as airplanes or as helicopters, and also machines in which some parts of their arrangement are altered for this purpose.
(1) Note. Aeronautical machines sustained at all times by both airplane and helicopter action, but providing for slight variations in the effect of one or the other sustaining agency, are classified in this class, subclass 6.
