Given that the 777 has the best DL longhaul product throughout the cabin and has no performance restrictions and considerable cargo capability, the 777 is a step up from a customer standpoint. ATL-NRT is also a 777 so it gives DL 777 service in two key hub markets, 747s at DTW and JFK, and 330s and 767s from the western gateways and a mixture of all at HNL.
The combination of the 777s and 747s provides the flexibility to right size capacity to the market; although some carriers are slowly adding back Japan capacity, there is still more capacity in Japan.
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as of now, yes, the LAX-HND flight is a 777.
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The 744s will likely be back at NRT next year unless DL decides to use them elsewhere on their network... only 2 so far are being removed from the fleet. If they move forward w/ the total cabin refits, the planes will be around until the leases expire - but I don't expect much longer than 5 more years.