The information regarding A380 fuel burn comes from Airbus, and only from Airbus. For example, "A380, which completed its ninth test flight over the weekend, has exceeded its fuel burn goals, Airbus sources told ATWOnline."
The statement from SQ
reads, "Airbus has demonstrated to Singapore Airlines' satisfaction that the engineering design of the A380 is sound. It has performed well in flight and certification tests, and the delays in its delivery have been caused more by production, rather than technical, issues." Thus SQ
is relying on what Airbus is telling them.
And then there's Airbus's reaction to Boeing claims regarding A380 fuel burn:
"They're saying it is 10% higher in fuel burn for both the Rolls-Royce and Engine Alliance engines, and that's huge," said A380 product marketing director Richard Carcaillet at the Asian Aerospace show in Singapore.
"We're talking about gross exaggerations..."
A380 product marketing director Richard Carcaillet.
At first I thought it was all relevant to the 748, but that's not the case because Carcaillet states the A380 will have lower fuel burn and trip costs than the 748, so his confirmation of higher fuel burn wouldn't make sense in only 748 context.
Exaggeration is stretching of the truth. That being the case then, according to Carcaillet, even with the RR
(at least) engines performing better than expected, overall A380 fuel burn is higher to some extent