Super, they are not mixing longevity methods. Your longevity remains the same its just the DAL payroll system is different. 1st of the month check is an advance on last months flying. 15th is the flight pay from the previous month. That's why you don't see changes right away. Your final paycheck should come the month after you retire so it all comes out in the wash. Now I'm only making an uneducated guess as to your issue. I may be totally wrong.