Originally Posted by
BraceBrace
I still have it in an old FCOM, it doesn't really explain anything. It states it is done for controllability reasons as there is excess power, and flap maneuvering speeds.
My only guess is a testing costs money issue. They might have discovered a reduced maneuvering capability at some flap setting anywere during the go-around with an engine failure (either Vref with landing flaps or any speed during the acceleration process with the selected flap at that point) below that specific weight. It then boils down to testing and that costs money. To save money they came up with one set of speeds below the weight, that works for all landing flap settings and incorporated these speeds in the manuals and FMC.
This is my suspicion, actually. Lots of great replies, thank you!