the second prototype pws-12bis (factory no. 358) was modified in 1931 to a role of an aerobatics aircraft. among others, fuselage sides were made flat and a rudder shape was changed. it received markings sp-ake and was flown mainly by lt. j. orłowski. in march 1931 it was used in a trip to estonia, and in april 1933 - to romania, bulgaria, yugoslavia, austria and czechoslovakia. then, both prototypes were used for several years as utility aircraft in aviation technical research institute (itbl). they were later stored in dęblin.