Sorry folks but a single passenger being moved from row 14 to row one on an A320 putting it out of trim
From a performance point of view the numbers moving are irrelevant. The problem comes when operating close to the trim limits (most commercial aircraft are balanced toward a medium passenger load). So a light passenger load can put you close to the trim limits as much as a heavy one.
The real kicker plays if you lose an engine on take-off, that's where you really feel an aircraft that's out of trim.
Move where you want for the flight just be in your seat for take off and landing please. I really don't care how much you moan.
