I've come up with an idea which might be completely wrong, but it goes like this: Since passengers are boarded via the left side of airplanes, engine # 1 is started up as last for a possible safety reason. Am I correct?
Since the RH
side is used for Servicing [Gallery,Cargo,Water,Toilet],Which is normally completed well before Startup.Hence by starting #2 first to save time,Last minute activity thru the Fwd Entry door can be accomplised safely.
On the old jets it was #4, #3, #1 and #2, as the L/H side was the "exit."
On Four Engined jets is the above sequence correct,Should there not be a stagger to avoid a pull on one wing.I would think #4,#1,#3,#2,can anyone confirm.