Some of the problems with the A380 come from the wing design: it has an unusually narrow wing for its weight (out of a desire to remain within the 80m box), alo

Some of the problems with the A380 come from the wing design: it has an unusually narrow wing for its weight (out of a desire to remain within the 80m box), along with the shaping of the wing being optimised for a heavier, long A380-900 that never came to market. An unusually large proportion of the drag comes from the wing on the A380. It's worthwhile looking at where Airbus proposed to improve the A380: * Densifying the main deck (going to 11-across in economy, still with 18" wide seats). This _alone_ in a typical configuration gives a 9% fuel-per-passenger gain. * They looked at new engines (derived from the A350, for example) which would provide a 5% fuel burn gain. * Minor wing modifications (new winglets and slightly reduced wing twist) which would provide a 4% fuel burn gain. * Longer maintenance intervals (so the aircraft spends more time in the air earning money rather). Other differences include that it holds much less freight in its belly than a 777 (a much larger proportion of its hold is consumed with passenger luggage), so you lose freight revenue. It's also worthwhile pointing out that engines are some of the most expensive parts to maintain on an aircraft, so by doubling the number of engines on an aircraft you make a very significant increase on maintenance costs. At the same time, you have the 777X lengthening the 777 (and increasing capacity) while reducing fuel-burn per seat, a much more versatile aircraft (an A380 will never be profitable on the major of 777X routes!), and more fleet commonality.