Jerricho,
My guess goes something like this.
EK 777's routinely fly to Heathrow at Max zero fuel weight, which in turn means they will be landing close to max landing weight. This gives a Vref of around 145-148 knots. Clean speed is then around 225-228, so when you ask for 220 kts, some guys take the flap and slow, others stay clean and settle for the extra 5-8 kts and some guys point out that they are a 777-300 and ask if 228 is OK.
Next step is when you ask for 180. At flap 5, which is the preferred congiguration at this point, the min speed for the -300 would then be somewhere between 185 and 188 kts, so all the above happens again. (The aircraft has the capability of using flap 15 which would be a nice compromise between drag and speed, but the company does not allow us to use this flap setting on approach).
On final, when you guys ask for 160 kts until 4 miles, the preferred configuration would be flap 20, giving a min speed of 165-168kts, so it would not be possible to slow to 160 without taking full flap. If full flap (flap 30 ) is taken, then the speed would reduce to Vapp which will be 150-153 kts.
Your confusion is understandable and will be further compounded by the odd occasion that the aircraft are well below max landing weght, which would allow them to comply with the standard speeds, no questions asked.
I would like to throw the question back to you. Does it cause you guys a problem if you ask for 220 and we give you 228 and when you ask for 160 on final, will 170 compromise the distance from the preceeding aircraft?
The way i see it, the problems we face in the aircraft (having to use more flap than is optimal, which in turn uses more fuel) could be relieved by giving -300 operators the instructions to slow down, at a position slightly earlier than the preceeding aircraft . That will mean the -300 slows down earlier which will increase the distance between preceeding aircraft, but can maintain a slightly higher speed which will close the gap again.
Personally i tend to fly at the optimum flap settings and accept the slightly higher speeds because it seems to me that due to the patterns that we fly into Heathrow, you guys (atc) always have the flexibility to extend downwind slightly if spacing is becoming a problem. Once on final however that option is not available and the speeds need to be followed by everyone, not just the -300's.
Could another solution could be for the -300 operators to pass their approach or Vref speed when they check in with approach or director, that way you will know exactly what speeds you can expect.
Cheers
The Rev