I'm not 100% sure but I just heard a story yesterday on ESPN radio (never did hear who it was that was saying this) but he said that they had inclement weather causing turbulence and thought they were going to die on a plane. A few days later they were playing in Milwaukee and they decided to fly the day of which he says was against NBA rules but they did it anyway and the team paid the fine. Well in the air the airport closed down due to weather and what should have been an hour flight turned into 7 hours of circling around trying to find somewhere to land. I guess they made it to the arena about 5 minutes before game time.
Anyway, I'm assuming if his story is accurate that the NBA requires that flights not be on game day.