The A340-600 is longer than a -300, more than longer than the Boeing 747-400 and longer than the A380, and has two emergency exit doors added over the wings. It held the record for the world's longest commercial aircraft until the first flight of the Boeing 747-8 in February 2010. The A340-600 is powered by four thrust Rolls-Royce Trent 556 turbofans and uses the Honeywell 331–600 APU. As with the -500, it has a four-wheel undercarriage bogie on the fuselage centre-line to cope with the increased MTOW along with the enlarged wing and rear empennage. Upper deck main cabin space can be optionally increased by locating facilities such as crew rest areas, galleys, and lavatories upon the aircraft's lower deck. In early 2007, Airbus reportedly advised carriers to reduce cargo in the forward section by to compensate for overweight first and business class sections; the additional weight caused the aircraft's centre of gravity to move forward thus reducing cruise efficiency. Affected airlines considered filing compensation claims with Airbus.