"3-I-5 A Pilot shall be paid on the first (1st) and sixteenth (16th) of the month for the preceding Bid Period. The gross pay on the first (1st) shall be one half (1/2) of his MPG for the preceding Bid Period and the gross pay on the sixteenth (16th) shall be his calculated earnings from the preceding Bid Period less the gross pay received on the first (1st)."