A typical unmanned aerial system combines an Inertial Navigation System (INS) and a Global Navigation Satellite System (GNSS) for navigation. When the GNSS signal is unavailable, the INS errors grow over time and eventually become unacceptable as a navigation solution. Here we investigate an image-aided inertial navigation system to cope with GNSS failure. The system is based on tightly integrating inertial sensor data with position data of image-featurepoints that corresponds to landmarks over an image sequence. The aim of this experiment is to study the challenges and the performance of the image-aided inertial navigation system in realistic flight with an Octocopter. The system demonstrated the ability to cope with the GNSS failure by reducing the position drift drastically compared to the position drift of free-inertial.