I have no idea, I had only been in the air for about 2 minutes (~85% bat), props were on tight, sky was sunny, winds calm-5mph. When I lost control it sounded like the motors were over-revving. It sounded like a gas powered model plane was buzzing by me. I was able to keep it about 90ft altitude and in the general area of a small pond in case it went down so it wouldn't hurt any people/ property. Then after about 30 seconds it made a high speed acceleration directly at the ground. Hit the ground about five feet from the water at probably 50-60 mph. The parts were all lying about 10-12 ft apart. I had successfully calibrated the compass just before flying. After doing some research, it sounds like this happens sometimes with NO explanation!