Ithought on quads you started 3421because when starting 3 if you had fire or anything fire service can approach from right then 4 for same reason then the other side 2 and 1 so fire guys are always able to get to the engines, and on twins number 2 because if fire or evac on start up then most pax will tend to go for the side they boarded and also clear area for fir trucks on right due to no air bridge