Originally Posted by JimInOhio

There's no good answer to this one. F9 operates from T5 while UA is in T1 and T2. Importantly, T5 is a separate security zone. There are airside shuttle busses that go to/from T5 to T1 and T5 to T3 but... there are reports that they limit those to who have a boarding pass applicable to the other terminal. However, people have gotten past this by saying "I'm going to the lounge in T5 (or T1 or T3)" and they've been let on.

Are you terminating at ORD or going onward the same day? That may help answer your question.