bob3,
I am assuming you have transitioned from a Boeing to an Airbus, I will try and answer your question using A320 data.
After selecting the destination runway and you are programming the APPR page on the MCDU you enter in the QNH, temp, magnetic wind/direction and MDA/DA, and you select if you are landing conf 3 or conf full.
The box will have come up with a Vls based upon you weight and configuration. Vapp is a calculated number, this is explained in the QRH on page 2.25.
For a normal landing (including a planned conf 3 landing) and you are doing an auto land or using auto throttle Vapp=Vls+5kt+wind correction. If you are not using auto throttle Vapp=Vls + wind correction.
The wind correction is 1/3 headwind (excluding gust) to a maximum of 15 kts.
Based upon the ATIS wids you enter on the APPR page the aircraft calculates what is know as Ground Speed Mini (GS mini) which is equal to Vapp-ATIS Headwind component (max of 10 kts). The aircraft uses GS mini as the reference speed for the inbuilt automatic windshear protection during an approach.
As you are doing the approach with managed speed the aircraft is constantly monitoring your ground speed and constantly changing the managed approach speed = GS mini + actual H/W (or T/W) component, but it is not less Vapp and not greater than Vfe.
When using managed speed the aircraft will keep an IAS of GS mini + actual H/W (or T/W), minimum of Vapp, maximum of Vfe.
As the aircraft is monitoring the airspeed and ground speed, you do not need to add the wind and gust factors as on a Boeing.
For an abnormal/emergency landing you add the approach speed increment to Vref. The approach speed increment is listed in 2.26 of the QRH. The approach speed increment is referred to as delta Vref.
Calculating what wind component to add for a abnormal/emergency landing is the where most people have trouble.
If your delta Vref is greater than or equal to 20 kts Vapp=Vref + delta Vref. For example if you have a green+blue hydraulic failure, delta Vref from 2.26 is 25 kts, and say for 68000 kg landing Vref = 138 kts, so Vapp=138+25=163.
If your delta Vref is less than 20 kts Vapp=Vref + delta Vref + wind correction, up to a maximum of 20 kts. For example landing at 68000 kg, Vref =138 kts (QRH 2.25) with a SEC 1+2+3 fault the approach speed increment from 2.26 is 10 kts. Say your landing on runway 36, and the wind is 060/12, wind correction = headwind comp is 6 kts, then Vapp=138+10+6=154kts. However if the wind was say 060/30, the wind correction = headwind comp = 15 kts, but the wind correction (15) plus the delta Vref (10) > 20 kts so Vapp=138+20 = 158 kts.
Edit : moved the wind from 030 to 060, thanks
[This message has been edited by Zeke (edited 18 May 2001).]