I have a dilemma. My sons H flies fine; however it doesn't want to land. It will SLOWLY descend and at about 6-8 ft. it descends no more. He has taken to flying back and forth with the thrust/yaw stick full down until about 1 ft. off the ground and then holding the start/stop button. It drops but it is on soft grass. I have gone through all settings, calibrations and all shows nominal (ok).