Regional airliner were replaced by progressively longer-range designs. In the immediate post-war era these were typically Douglas DC-3s, although even the De Havilland Dragon Rapide biplane airliner remained in service for some time. This "hand-me-down" process of supplying aircraft continued with designs like the Convair 440, Douglas DC-6 and Vickers Viscount also serving in this role while the first jets were introduced. By the mid-1950s, demand for even more economical designs led to the production of the first custom feederliners. These were almost always turboprops, which had fuel economy on par with piston engine designs, but had far lower maintenance costs. Often
Kuznetsov NK-12 the NK-12MA. The NK-12 remains the most powerful turboprop engine to enter service although the Progress D-27 and Europrop TP400 have come close to this (in 1982 and 2005 respectively). Another engine of similar size, the Pratt & Whitney T57 with 15,000 shp and 5,000 lb jet thrust, ran 3,100 hours before being cancelled in 1957. The NK-12 powers the Tupolev Tu-95 bomber and its derivatives such as the Tu-142 maritime patrol aircraft and the Tupolev Tu-114 airliner (with NK-12MV), which still holds the title of the world's fastest propeller-driven aircraft despite being retired from service in 1991. It also