A quick question whilst on this topic. Would you apply these corrections to the wind vector reported by tower whilst commencing approach or to the wind vector calculated by the onboard computer? In the latter, wouldn't it keep changing as you're approaching the ground so would need to constantly adjust your Vapp?
I had a discussion with my captain about that a week ago. On our MD11's the wind indications on our respective ND's are slightly different due to IRS drift differences, and the closer you get to the ground the more inaccurate, even to the point of being totally useless (indicating eg. 3 kts head on the left side, 4 tail on mine). We are supposed to use the tower wind, but this isn't always accurate either, depending also on the airport where you're flying into. We just try to be on the safe side, that's all really.
BTW, our company policy is either the full wind above 20 kts, OR 1/2 gust factor, whichever is HIGHER. Minimum Vref+5, maximum Vref+20.
G.