what is the smallest aircraft available flying from pittsburgh to baltimore arriving on may seventh 
return flights ;return #1 from pittsburgh ;return #2 to  baltimore ;return #3 arriving on may seventh ;return #4 that  are available ;return aircraft of #5 ;return size of #6 ;return #6 where #7 is  the  smallest
['select', 'filter', 'filter', 'filter', 'filter', 'project', 'project', 'comparative']