One method for calculating a firm's free cash flow (FFCF, or CFFA) is to ignore interest expense. That is, pretend that interest expense (IntExp) is zero:
FFCF=(Rev−COGS−Depr−FC−IntExp)(1−tc)+Depr−CapEx−ΔNWC+IntExp=(Rev−COGS−Depr−FC−0)(1−tc)+Depr−CapEx−ΔNWC−0