Thanks for all your replies.

Now this is purely a hypothetical question which could apply to any seniority based airline. I'm not suggesting that we're in this situation, but just say there is an immediate vacancy for an FO to upgrade to Captain. The last person to upgrade had a seniority number of 500. FO 'A' has a seniority number of 501 but has not yet met the upgrade requirements. FO 'B' on the other hand has met the requirements but has a seniority number of 521. The 20 FOs ahead of him/her are also yet to meet the requirements for upgrade.

So what would happen in this case? Would FO 'B' be offered to upgrade due to the urgent need of the company for a Captain or would the company wait until FO 'A' has met the upgrade requirements even if this meant parking airplanes for the next 6 months?