The later production Tu-144 versions were more refined and competitive. The Tu-144D had Kolesov RD-36-51 turbojet engines providing greater fuel efficiency, cruising speed and a maximum range of 6,500 km,[287] near the Concorde's maximum range of 6,667 km.[288] Passenger service commenced in November 1977, but after the 1978 crash the aircraft was taken out of passenger service after only 55 flights, which carried an average of 58 passengers. The Tu-144 had an inherently unsafe structural design as a consequence of an automated production method chosen to simplify and speed up manufacturing.[289] The Tu-144 program was cancelled by the Soviet government on 1 July 1983.[287]