ak_code bnum        craft_type
AA      RA-85205    T154
AA      RA-85162    T154
AA      RA-26305    AN26
BB      RA-85343    T154
CC      RA-96002    IL96
CC      RA-96012    IL96
CC      RA-96016    IL96

select ak_code,craft_type from crafts
 where ak_code in(
   select ak_code from crafts
    group by ak_code
   having count(bnum)>1
 )
group by ak_code,craft_type

ak_code  craft_type
AA       AN26
AA       T154
CC       IL96

ak_code  craft_type
CC       IL96

select ak_code,craft_type from crafts
 where ak_code in(
   select ak_code from crafts
    group by ak_code
   having count(bnum)>1                 -- Количество бортов более 1 (аналогично count(1))
      and count(distinct craft_type)=1  -- Только один уникальный тип ВС
 )
group by ak_code,craft_type

select ak_code,max(craft_type) from crafts
 group by ak_code
having count(bnum)>1
   and max(craft_type)=min(craft_type)