An extra set of wheels
Two versions of the long-range Airbus A340 are in service with Lufthansa. The stretched A340-600 carries 306 passengers, its little sister, the A340-300, carries 221. It joined the fleet in the early 1990s and was the first four-engine, wide-bodied jet produced by Airbus. One innovation was the fourth set of undercarriage wheels in the middle of the fuselage. When fully loaded, the A340 is a great deal heavier than the similar, two-engine A330, which doesn‘t have a reinforced undercarriage.
* September 2016; ** with max. number of bookings; *** Configuration may vary