TIM, we have to be careful with our words here. First, my use of ‘windshear’ would not cover the big windshear events; thus, wind variation during gusts and wind change with altitude might be more appropriate.
Second, your use of ‘adequate’ depends on the context.
For the redefined conditions above, 1.3 Vs should be adequate during the approach and landing in benign conditions (low turbulence), both for large commercial and for GA aircraft. However, without a specific reference and little GA light aviation experience, I don’t know if this is adequate for operations in all conditions.
Commercial aircraft encountering a gust or shear during the flare, might require additional speed to offset engine response, handling qualities (response time), etc. This leads to the debate as to whether speed increments are carried into the flare or not, or that gusts and shears are of less concern during the flare – then there is ground effect, view over the nose, tail strike … etc, etc.
Extract from
AC 25-7 Fight Test Guide for Certification. Para 19, re 25.125.
“
The term VREF used in this AC means the landing threshold speed (i.e. speed at 50 ft. height) scheduled in the AFM for normal operations. The minimum value of VREF is specified in FAR 25.125(a)(2) as 1.3VS, which provides an adequate margin above the stall speed to allow for likely speed variations during an approach in low turbulence. ”