Very light weight 777F Vref speed bump
OK, reposting this as a separate question as I think it is getting missed as part of another thread:
wondering about that 777 approach speed bump. Vmca is approximately 136-137 KIAS and so, so depending on flap settings you'll hit the floor at weights something below 460,000 pounds . But something else happens at the lighter weights that I cannot find. I show Vref go from 136 at 340,000 pounds to 143 at 339,000 pounds and below. I have yet to find a satisfactory explanation for this.
777F. Here are flap 30 values. Notice the below 340k line. Below 340k the speed is the same for all flaps settings. It does decrease with altitude but why the increase below 340K?
Weight
(1000 lb)
Pressure Altitude (ft)
0 2000 4000 6000 8000 10000
780 184 184 184 185 185 185
740. 178 178 178 179 179 179
700 172 172 172 172 172 173
660 164 164 164 164 164 164
620 158 158 158 158 158 159
580 151 151 151 151 151 152
540 145 145 145 145 145 146
500 140 140 140 140 140 140
460 137 134 134 134 134 134
420 137 134 130 128 128 128
380 137 134 130 126 121 121
340 137 134 130 126 121 116
Below 340 143 140 137 134 132 128