The actual VAPP value is calculated as follows:
Assuming the tower reported steady state wind is entered into the MCDU APPR page.
VAPP = VLS plus 1/3 of the tower headwind component. The value of VAPP is limited so that it is never less than VLS + 5 or more than VLS +15.
As a result, VAPP is increased above its minimum value for runway headwinds above 15 knots. VAPP correction is not increased further for headwinds exceeding 45 knots.
The groundspeed mini function does not change VAPP, instead, it increases the target (bug) speed when the headwind is greater than the expected landing headwind - the wind that VAPP was based on. This is done so that if this greater headwind disappeared all at once (windshear), the airplane would be at VAPP not VAPP minus the loss of wind.
Tomorrow we will see what happens when we initiate a go-around.
Enjoy the journey!
XOX Karlene
Ahhh - this is good information to know. Not only is weight a factor but also based on wind speed. All interesting how these factors come into play and yes, I am glad that we are not the ones calculating VAPP.
ReplyDeleteYes, Airbus figures in wind. Boeing doesn't. I don't think. It's been a long time. But, thankful we don't have to calculate it.
DeleteHi Karlene,
ReplyDeletecould you please confirm that you meant to imply that vapp is increased above the minimum if the runway headwinds are greater than 15kts? I think that should be the case when the headwinds are less than 15kts. I'm new to this aircraft, still trying to understand the automation and systems so just want to get things right.
thanks.