Turkish Airlines has revised planned Airbus A340-300 operation for winter 2015/16 season, effective 25OCT15. A number of previously scheduled A340-300 operational routes will also see A330 operating, or being replaced by A330.
Istanbul Ataturk – Boston eff 01NOV15 Airbus A330-300 replaces A340-300, daily service
http://airlineroute.net/2015/07/17/tk-343-w15update1/
However, booking this flight online still shows the A340