Jack...what airline in the US would that be???? When your captain number comes up you can defer or upgrade. By defering you increase the value of your seniority number as a captain at a later time...you don't drop to the bottom of the captains list! Hence, you can be a senior FO one day and be a senior captain the next as in FD. Further, what airline in the US hires DECs?? Sorry mate but your logic flawed. I am not aware of any airline in the US where you loose relative seniorty by upgrading. So be careful in painting with such a broad brush...perhaps in some fractional programs that may be the case, but no legacy airline will practrice what you speak.