Method of permanently joining composite parts made from thermoplastic material, arrangement of composite parts, and aircraft

A method of permanently joining first and second composite parts of an aircraft together, the method comprising:

• providing:
• first composite part that is a skin element of the aircraft and is made from and comprises a thermoplastic material:
• a second composite part that is a profile element of the aircraft and is made from and comprises the thermoplastic material;
• wherein an orifice is in at least one of the first composite part and
• the second composite part;
• positioning both of the first and second composite parts such that a portion of whichever of the first and second composite parts comprises the orifice is adjacent to a portion of the other of the first and second composite parts;
• injecting a melted thermoplastic material through the orifice to contact the first composite part and the second composite part in a contact area, whereby to melt together surfaces of the first composite part and the second composite part in the contact area;
• and
• solidifying the melted thermoplastic material in the orifice and in the contact area to permanently join the first composite part to the second composite part.