Send an e-mail to audit. They answer them and would like to solve this before the occurrence rather than after. You will find out whether it will go thru without incident. Hopefully it meets what we are authorized in the contract. If you don't get the answer you like and have doubt, call/e-mail ALPA.

That said--

I believe that in order for you to get the first class fare as the authorized fare for reimbursement, your actual flight (deviation or scheduled) must meet the parameters. 5 hrs or 11:30 duty authorizes first class. Otherwise the amount over coach would be classified as a personal expense no matter how much you have in your bank.

This is distinct from the class of fare that your scheduled DH accepted fare is based upon. The scheduled DH accepted/approved fare is based on what class of service is authorized for the scheduled DH. I don't know what happens when first class is sold out on the scheduled flight. Do we still get the first class fare for bank even though we are booked in coach? Not sure about this.

If the deviation DH is authorized a higher class of service than the scheduled DH, your bank does not jump up to first class for that DH. But you can still get reimbursed for first class on it if you have other, unused, bank monies available.

I've never done this so I am going on what limited knowledge I have. Next week there will be an FCIF outlawing it!