woodpecker
In the first instance this impacts ETOPS in the way that re heat mentioned, Even though it was not classed as an ETOPS sector or a/c, the B747 has the same basic engine as the B767 and as such any ifsd counts against the engine and hence impacts on the ETOPS rating.
As for the fuel, the no 2 tank had much the same as the no 4 which was 2.5 tons, as for fule feed, I am not a 747 guy but I believe that the centre and tail are used first and then the reserves then main tanks, the problem was that with the engine shut down, they were only able to get fuel out of the the no 2 tank using the over-ride pumps and they shut off at about 3 tons so they could get no more out. Yes I know there is a discrepancy in the figues but that is what the guys were looking into and will be for some time I guess.