Don't know what happened . I was careful not to cut into the wing. I called Horizon and told them about it . They asked me to send the plane to them so they could examine it to see if there was any structal /design.or factory assembly problems. I waited for a reply, then about 10 days later I received a new plane. The note that was with it said they could not find anything that may have caused it . But you can't expect for them to say it was a design or factory assembly problem. Anyway I also told them about the aluminum motor mount and they wanted it also. Have not heard from them about that. They said they would send me a new mount but I made one from steel and told them not to send it that I felt better with the steel one..