The deviation bank is the total $ amount for a pilots' scheduled dead heads for the month. He can deviate from the scheduled transportation and use our corporate travel office (or make arrangements on his own, but must save the receipts) to buy a different ticket for travel to or from the trip. There are some rules obviously, i.e. the travel has to be within 3 days of an operational trip, etc.
At the end of the month when the pilot files his expense report, the the scheduled travel $ amount is his deviation bank, as long as his deviation travel tickets don't exceed his bank amount, he owes the company nothing; if they do exceed then he must pay the difference.

Would be nice if the bank was at least quarterly instead of monthly. Rumor has it that this was addressed in our new TA.