A low cost operator may utilize an aircraft for up to 20 hours per day at peak periods, this involves 2 or 3 crew operating the same aircraft in a 24h period. One crew will be on annual leave or sick, another 1 or 2 crew will have their rest period. Maybe one crew will be on recurrent training or auxilliary duty. So depending on aircraft usage, you might need 6 crew per aircraft. you get 2 pilots per aircraft operating at anyone time, you can make yourself the rest of the calculation.
