With the B744 I had been in the habit of subtracting 10 tonnes from the gross weight at 500nms before arrival airport to account for the fuel burn from the point of setting landing flaps to landing, to set my Vref for flaps 30.

 

With the B777, should I subtract an amount (say ~8 tonnes) if I am setting my landing flaps at 500nms from arrivals airport still, or just use the Vref value shown for flaps 30?

Why not? That seems reasonable to me to use the expected weight.

Not sure what you mean. The progress page gives you an estimate for arrival (of course with the expected approach procedure and Runway acivated). Just type that into the Ref Page and you got your Vref.

Can't you just wait until descent to finalize your Vref?

 

If not just use the progress page as mentioned by Chris above.

Why 500nm before destination? It's three clicks, just do it at the top of descent.

You would normally be using some form of onboard performance software for landing. However, you can use a simple formula (metric tonnes) you should already know what your planned landing weight is

 

Vref30 = (Landing Weight in Tonnes / 250) X 151

 

Remember the FMC gives Vref + 5, you can increase that upto Vref+ 20 for wind corrections

Current fuel in tanks 10.0

FMC calculated fuel at landing 6.1

 

10.0 - 6.1 = 3.9

 

Current Gross Weight: 189.5 Tonnes (189500kg)

 

189.5 - 3.9 = 185.6

 

 

Don't round figure it. Actually calculate it. Also, do it after the arrival details have been entered and, if you're doing it, after the Decent winds forecast have all been entered too. That way you're not guessing "about 8 tonnes less" - you're actually entering the actual landing weight you will be touching down with.

 

Current Fuel on Board, minus FMC Predicted fuel at arrival.
Take the difference and subtract that new number from the Current Total Gross Weight.

 

That is your calculated landing weight

 

Enter this new "Calculated Landing Weight" number into the FMS "Current Gross Weight" field on the Vref Calculation page of the FMS.

The FMS will calculate V-speeds based on the entered number.

 

If you leave the Vref calculation page and come back to it (ie go to legs page and back) the manually entered number will be gone, and be replaced by the actual current Gross Weight.

 

You can test this by entering the calculated weight really early, when there's a large difference between calculated and current. Current Vref flap 30 = 142
Updated Gross weight to calculated Vref Flap 30 = 137

 

Go back to legs, back to Vref.

 

Your hard selection will still be the same (Flap 30 = 137), but the 'suggested' Flap 30 Vref will be back to 142.

Thanks gentlemen. I shall do the more accrate calculation in future.