Excerpt from an interview with Sammy Hagar on classicrockrevisited.com:
Jeb: Last one: I heard that Eddie and you got into a fight in an airplane, while in the air, and Eddie actually tried to smash out a window in the plane. Is that true?
Sammy: Yes, it is true. He tried to smash the window out with his hand until he hurt his hand. Then he tried to smash it out with a wine bottle until Alex jumped up and took the bottle from him and calmed him down. I was going to quit the band the next day, but there were forty more shows and I couldn’t do that to the fans. I thought that it was not cool to burn the fans. I knew they [Van Halen] would make me the bad guy. I refused to fly with the guy ever again. He was completely out of his mind drunk. He was completely wasted. He was so wasted that he was actually stupid enough to take twelve people down. People that act like that shouldn’t be allowed to fly on airplanes, and they probably can’t, but we were flying privately. I said, "The only way I will continue to do this tour is if I have my own airplane." They paid for my own airplane.
Jesus. What a douche.