The challenges associated with riveting contoured aircraft skins include achieving and maintaining perpendicularity of the riveting machine. One of our customers has discovered an improved method which utilizes ultrasound to position a multi-axis riveting machine, and/or the aircraft structure, so that it is perpendicular to the contoured skin. Since the rivets hold the aircraft together, the integrity of rivet fastening is critically important.This ultrasonic method uses a non-contact ultrasonic distance measuring system, the DMS-1000, from Ultrasonic Arrays, Inc., of Woodinville, Washington. Three DMS-1000 transducers are mounted around the riveting head of a Gemcor Drivematic Multi-Axis Riveter. The transducers measure the distance to three points on the aircraft skin. These three points describe a plane, enabling the rivet machine to calculate the planar orientation of the panel relative to the riveting spindle. The distance data is then transmitted to the machine controller where the information is used to calculate the orientation of the rivet machine and correct alignment. The operator also has the ability to manually adjust the machine and/or the aircraft structure, until all three gauges read the same distance.The non-contact, ultrasonic method was chosen because it eradicates human error, offers productivity improvements, and eliminates surface marring and scratching.