Questions to B747 drivers

[givmi]

Hello I am new to the B747,

Got a few questions:

Let's imagine we have an engine failure on engine 4, would you open the crossfeed valves 1+ 4 ?...the QRH does not tell you to do this but otherwise the fuel is trapped?

Are the FMC performance predictions correct, after having lost 1 engine, if you select ENG OUT prompt on the VNAV page.

For any other non normal configuration (Flaps stuck etc) the performance predictions will of course not be correct…but is there a quick way of calculating your ETA and Fuel up on arrival.

Below is what I used so far.....but is there any faster way on the 747

Time= Distance/GS then multiply it with current FF to get Fuel required.

Fuel onboard-Fuel required= Fuel upon arrival

(if you enter your GS on the VNAV page it will give you a correct ETA?)

Thanks