In the days following their takeover of most of Air Berlin’s routes, Lufthansa has deployed their 747s on certain flights between Berlin and Frankfurt to help move passengers between hubs.
Initially, plans called for the 747s to stay on the route for certain flights until November 30. Due to load factors, LH has now extended this strategy to at least December 21, primarily to help manage increased passenger traffic during the Christmas season.
Keep in mind that not ever flight between Frankfurt and Berlin is operated by a 747. In fact, only 28 flights in total will fly between the 2 cities between December 1 and December 21. All other flights between the city pair will be operated by A321 aircraft.