The A-380 is a great aircraft, but it is still a failure.
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B-747.
1. The 747 was released back in 1970. That was the age of big full-service airlines. Fares were high - with luxury service on board aircraft. Large airlines could afford to buy/lease large aircraft. Only rich people flew in airplanes, paying a lot of money for the luxury. The rest...
more... of us travelled in Sleeper class with a "hold-all" for bedding. We used to be impressed of those who flew in airplanes.
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2. Now many airlines have ALREADY bought their 747s in the 1980s, 90s. Those that are already bought have to be flown. That's why we still see a lot of 747s.
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A-380.
1. A-380 was released in 2005, maybe a little too late. Fuel prices were high - Iraq war. The world economy (in the developed countries) collapsed in 2008. Airlines took a big loss. So could not afford to buy expensive aircraft. At this time, the well-funded Emirates is the main loyal customer of A-380. Emirates is well-known for its standards of luxury - it is consistently rated the top airline in the world in terms of passenger comfort and amenities. #2 in the world is Singapore Airlines, which also buys A-380, which exactly fits this luxury profile.
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2. 4 engines of A-380 are expensive to maintain. Twin engines are easier to maintain and are usually more fuel-efficient.
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3. If a large aircraft like A-380 flies at 80% capacity, then it will be a net loss for the airline. Filling up large aircraft is tough.
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4. Emergence and dominance of low-cost airlines, who prefer smaller twin engine aircraft like 737 and A-320, which are easier and cheaper to maintain.
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5. Low-cost airlines usually fly point-to-point between smaller airports - carrying less people (as explained by Dark Lord). A-380 will not fit into smaller airports.
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In summary, while there is continuous steady demand for A-320 and B-737, it is the end for large 4-engine aircraft like A-380 and B-747. A-380 cannot keep up manufacturing just to supply one customer like Emirates. Semi-large twin-engine aircraft like B787 and A-350 may still have a market. Many B747s will continue to fly, because they were ALREADY bought in the last century. Most probably, there will not be any new orders for 747 either.
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Mangla-ji and others may point out any errors in the above analysis.