320 to 321, always a trap
We have this situation a couple of times a month, and my first thought is always pax seating and underfloor loading. Followed by fuel required.
I always discuss the pax seating with the Cabin Manager and get them to check if it “looks ok” before we close the door. (Ie: pax distribution across all 3 zones.
My company has their own iPad based loading system, which is far from perfect and doesn’t populate any of the Airbus performance data.
So it is always a challenge, and requires extra vigilance for loading and operations.
That doesn’t stop these similar events from happening, but touch wood, I’ve managed it up to this point.
They were lucky this time, it could have been a lot worse.