Found this explanation from someone who must be an OAI pilot:
"The website does not say, but I am betting this is for the 76. We have gained two aircraft within the last two years and have two more coming in 2020 (from an previous fleet size of 9) . The company has gone through the seniority list and have awarded upgrade to all who have their bid in and and meet the company qualifications. A lot of hiring has occurred in the last year and a half (since the new contract) so many of the FO's are new to the plane and/or company and realise that they may need a little more seasoning before moving over to the left seat, so many are bypassing. Training here is no joke and the attrition rate for upgrade is a valid concern. We have verbiage in the contract that will open up lateral moves to all in case of new hire captains, but we haven't heard a word from the company or union on this as of yet."
