Traditional User/Maintenance Manuals provide useful information when dealing with simple machines. However, when dealing with complex systems of systems and highly miniaturized technologies, like UAVs, or with machines with millions of parts, a commercial aircraft is a case in point, new technologies taking advantage of Augmented Reality can rapidly and effectively support the maintenance operations. This paper presents a User/Maintenance Manual based on Augmented Reality to help the operator in the detection of parts and in the sequence to be followed to assemble/disassemble systems and subsystems. The proposed system includes a handheld device and/or an head mounted display or special goggles, to be used by on-site operators, with software management providing data fusion and overlaying traditional 2D user/maintenance manual information with an augmented reality software and appropriate interface. This device is connected by internet to a maintenance centre located in the aircraft manufacturer facilities. The on-site operator can directly access to multimedia content and historical information and can be helped or guided remotely by expert engineers residing at the manufacturer company offices. This resource may exploit Computer Aided Design and Product Data Management PDM remote facilities to prepare additional and specific 3D graphic content, supported also by a video and audio streaming from the camera and microphone of the on-site operator's handheld device. The proposed solution has revealed a number of significant advantages compared to the currently used operations: there is no need for preparing animations and graphic content for all the required maintenance sequences. The expert engineers and designers can both be involved directly in the maintenance tasks, a useful mean of feedback to evaluate the design for further projects or for project improvement. Additionally, the sensitive data is not shared outside the company since data is transmitted for visual display but it is stored on a secured location.