First, note that you will probably only get GPS lock outside (if you’re very near a window or are lucky enough to have strong GPS signal and a radio-transparent roof, you may be able to get lock inside). For a cold start (power on), it make take three minutes or more. In order to get a GPS lock you need to have your HDOP value under 2.0. You can see this value by connecting your IRIS to Mission planner on the Flight data TAB.
If you can’t get GPS lock outside after many minutes please note that this depends on a number of factors including Sky blockage and weather. Click here to find out more on how the GPS works.