I flew IAD-SFO last night on the United and had my headset tuned to Channel 9 the whole way. After we cleared IAD departure, we were handed off to the Washington Center, then the Indianapolis Center. While we were under Indy's stewardship, I kept hearing controllers instruct other flights to "contact Indianapolis Center on [frequency]."
This confused the crappicus out of me, because if we (United 205) were in contact with the Indy Center, that (ummm, ostensibly?) meant we were on a frequency being USED by the Indy Center. Why then would I hear flights on that same frequency, being handed off to the Indy Center? Is it that sometimes a Center asks you to switch frequencies while remaining under their control?
'Cause the same thing happened while we were tuned to K.C., Denver, Salt Lake, and Oakland. I think it happened on North-Cal approach as well.
Someone please edumucate me. Thanks.