Charter of large aircraft will will fall under 121 if we're using the same definition of charter - a company advertises "We'll take you where and when you want to go." Since there is no schedule it falls under 121 Supplemental. Say a football team owns a plane to travel to games. The only people riding on the plane work with the team or could be family or media invited along. You and I can't buy a ticket on that flight even though we're going to the game. That would fall under 125. There aren't that many 125s around. There are some that have contracts with sports teams flying baseball teams during the summer and hockey during the winter. Donald Trump's plane would fall under 125.