Air India normally uses it’s 777 fleet for Direct US flights because the 787 is extensively used for every other International flight. Any International flight other than US flights are operated on 787s and as a result, no 787s are left to use for US direct flights. Air India owns 787–8s which have a slightly lesser range than the 787–9. Their 777–200LR has a massive range and can travel to virtually anywhere. If Air India decide to use 787 on US flights, then they will have to use 777 on smaller routes like DEL-BKK, BOM-LHR, DEL-HKG, BOM-SIN. The 777 on such routes would be inefficient and would raise costs. Also 787 carries much less passengers compared to the 777. I guess the main problem is the lack of availability of 787 aircraft to assign US flights. I guess they should stick to using 777 on US routes for now and later replace it with 787–10 which would hinder only the capacity. The 787–10 is very similar to the 777–300 and has much less operating costs. Air India should consider replacing their 777 fleet. Also their 777s are old and tampered.
Source – Quora