Cross the threshold...
Target speed is usually 1/2 the steady state wind plus all the gust factor (if any). This speed is to be held until crossing the threshold (actually
50 feet). Total additives not to exceed 20 kts...
Example: Vref is 120
Landing Runway 10
Reported surface winds: 060/12G22
So, take half of the 12, which equals 6....and all of the gust factor, which is 10 (22-12)
Vapp = 120 + 6 + 10 = 136
Note: This is a TARGET SPEED....it's not a minimum speed or maximum speed...it's what you try to hold...plus or minus...based on the turbulence and wind speed kicking around.
Speed to reduce to as you're crossing the fence:
120 + 10 = 130
(10 is the gust factor...which you are to hold crossing the threshold, going into the flare)
The idea is to touchdown at a speed not below Vref...or thereabouts....so, you have to be prepared for a loss of the gust factor as you go into the flare...thus, you hold the extra speed (in this case the gust factor of 10 kts). In theory, you could lose 10 kts of wind...lose 10 kts of speed...at the worst moment (in the flare)...that's why you keep the gust factor as you cross the threshold.
In the Airbus, we normally use 'Managed Speed' .....so, these calculations are made for you...a different algorithm.
Fly safe,
PantLoad