Scan2Map is an airborne remote-sensing system developed under the lead of the TOPO lab at the EPFL. Typically operated aboard a helicopter, it is dedicated for small mission areas (a few square kilometres at the maximum) and offers a sub-decimetre accuracy of the derived mapping products (orthophotos, digital surface- and terrain models). To achieve this high quality independently from ground control, Scan2Map relies on GPS/INS for determining the parameters of exterior orientation of the image sensors (i.e., a digital camera and a Lidar line scanner). In order to guarantee the complete coverage of a given area of interest, a detailed flight plan needs to be elaborated and it is essential to follow this plan as closely as possible during the flight. However, certain types of problems may remain hidden during the data recording, e.g., insufficient Lidar coverage due to poor ground reflectance. To avoid suchlike situations, an online monitoring tool is currently under development that allows assessing the quality of the recorded data while in the air. Among other calculations, this tool requires the real-time processing of the GPS/INS data. The paper describes the principles of airborne mobile mapping by Scan2Map, discusses cer-tain aspects of the real-time GPS/INS processing, and shows some initial results obtained during the development of the quality-assessment tool.