My mom was going to fly UA ORD-HKG, but she's on standby. She said there weren't many passengers but NO standby passengers were allowed on the plane because they needed the extra weight for their cargo. Also, something about wind conditions and that if the airplane is too heavy they can't bring their nose up too high or something because of the wind.
She was tried this flight for 2 days and didn't get on so she finally decided to go to Tokyo instead. So, what does all this mean? Were these flights really too unsafe to fly the extra standby passengers? However, it is winter! So I guess so.