All airline companies operating in the State shall make an annual property tax return on or before the 15th day of April in each year for the preceding calendar or fiscal year of their flight equipment to the department. Each type and model of flight equipment shall be separately returned, valued and apportioned as herein provided.

Provided, However, That the first report of airline companies shall be filed on or before October 15, 1976 and any tax due shall be paid by December 31, 1976.