Originally Posted by IO540
The idea behind Va isn't so much to do with max elevator deflection as with the capability to withstand vertical (upward moving) gusts.
The idea is that if flying at or below Va, the wing stalls, thus disposing of the load, before reaching the standard +3.8g (or whatever) design limit.
The stall speed, Vs, varies with aircraft weight. An aircraft loaded to MTOW might stall at 60kt; the same one loaded say 20% below MTOW might stall at 70kt (I don't recall the formula).
Therefore, the same aircraft, if lighter loaded, will need to fly slower (i.e. closer to its actual Vs) to be at Va.
I thought it was to do with both situations. My initial question was if a lighter plane flew faster before it stalled that should be fine since it was lighter - for the same load factor the wings can be stressed more since the weight is less. However, Rivet Gun has kindly pointed out that there are other load bearing parts that indiviually may exceed their ratings in this situation.