You cannot preference bid jet to jet in the same seat - in example: the 175 is DFW only right now. You're an FO on the 175. Your girlfriend dumps you and you're out of the apartment and you want to move back to ORD where you are from.

You cannot bid ORD/FO/E145 if a vacancy bid opens for that. You're stuck in DFW/FO/175 until: A) A 175 base opens in ORD and you are able to get a bid award for that base, B) A vacancy bid opens in which you are able to upgrade to ORD equipment, or C) You are displaced and able to hold ORD equipment as a displacement preference.

The displacement into the 175 with our current situation was odd. There were FO's that bid the 175 as new equipment and there were FO's that bid it as a displacement pref. I think there were instances where a junior FO got the 175 ahead of a senior FO due to the way the displacement and pref bids are run, but someone with better knowledge of how that all shook out will have to explain it.