I flew several Ground Station missions this evening from a high vantage point across the tree tops and over the neighbouring lake etc. All flown with waypoints set at 30m. After the first 2 flights, each of 1.5km distance, I decided to do one last flight in the opposite direction, taking off on the rear patio, climbing to a first waypoint directly overhead at 20m then on to further waypoints all at 20m altitude. Unfortunately, I did not think to recheck the home position altitude after the first 2 successful flights. This video is the result. http://youtu.be/77u64x9qeNs Basically, for some strange reason, after the first 2 flights the home position altitude had changed from 0ft to 30ft so climbing to first waypoint it only climbed to 10m, as opposed to the programmed 20m. My brain did not engage quickly enough to flick the S1 switch to Atti position prior to attempting to pump in additional height on the left stick before, bang!, it hit the roof parapet and fell to the ground. Luckily it fell into a bush. Had it fallen 12 inches either side it would have crashed onto the paving slabs and been toast. As it was, a quick reboot, correct altitude set, and off it went on it's merry way. So so lucky no damage to props, camera or gimbal. lesson learnt. Follow a pre-flight check list before each and every flight.