After loading the plane, passengers check-out and embarkment, the AZ517 scheduled flight to Milan was ready to tow from the A5 stand onto the taxiway. After going through standard pre-flight procedures, the PIC received an ATC clearance to be towed to B1 taxiway and radioed the ramp control to attach the tractor. Using a standard prescribed way, the ramp controller asked the tractor operator to come and attach the nose undercarriage to push back the plane from the embarking bridge to taxiway B1. Simultaneously with removing the embarking bridge from the plane, the tractor driver drove to the airplane, fixed the front undercarriage leg onto the tractor platform and waited for further oral instructions from ramp control. The ramp controller checked visually that the airplane door had been shut, the tractor attached properly and the safety pin of nose wheel steering disconnection had been properly in place. Then he advised the PIC that the plane was prepared for push-back. The PIC released brakes, issued the instruction based upon ATC information to push back to taxiway B1 and the push-back commenced. During the push-back the PIC started both of the plane?s engines. After reaching the right position on B1, the plane was stopped and the ground controller passed information about end of push-back to the PIC, who braked the plane to stop. The tractor driver began to release the front undercarriage leg. At this moment the ground controller received from PIC the instruction to tow the plane from taxiway B1 to taxiway B 2. The ground controller passed the oral instruction to the tractor driver who attached the plane again, getting it ready for another tow. The brakes released, the plane was towed in a left turn perpendicularly onto taxiway B2. When aligning the plane to be in line with B2 direction, the tractor made a sudden tight right bend so that the tractor began to turn under the right-hand side of the plane. This manoeuvre caused the plane to pass the tractor so the latter might have begun to brake. The plane moved in its direction and drew the tractor in behind the front undercarriage leg. The ramp controller, who was standing on the tractor step, fell over to the ground. As he fell down, radio contact with the PIC got broken so the ground controller signalled with hands to F/O to brake the aircraft. Before the plane had stopped, the tractor driver?s cabin hit the fuselage starboard and the front undercarriage was pulled out of the tractor tongs. The airplane continued to travel with the damaged undercarriage perpendicularly towards taxiway B2 turning gradually to the left. After travelling 7 m the pilot braked the plane to a standstill and switched the engines off. CONCLUSIONS The probable cause of the incident was the driver?s unconscious reaction to the abrupt right turn manoeuvre to reach the B2 line. Braking and slowing down the tractor caused it to be drawn under the plane due to the plane?s inertia and mass resulting in damage to both the plane and the tractor.