Bus at remote stands
As I live in London, memory suggests this occurs often at STN, but this is probably just because I see more of STN than anywhere else.
Occasionally an FR plane will have to park at a remote stand, sufficiently far from a terminal to necessitate a bus ride rather than a short walk. 189 people necessitates 2 buses rather than 1. Some airports are pretty good at having these buses close to the plane before the plane has even finished dropping its steps to the ground.
Some passengers manage to get down the steps onto the ground pretty quickly and the 1st bus fills rapidly. Neither bus however will move until ALL the pax are off the plane and someone in the crew has given an 'all clear' signal.
If the first of the 2 buses already has 100 people inside, why does it need to wait until the very last passenger has got down the steps and onto the 2nd bus before driving off ? Why can the 1st bus not proceed to the terminal and leave the 2nd bus to collect up those who need more time to get from plane to bus ? At the very least, this would free up the bus earlier for its next use, never mind processing pax more quickly through the airport. It is after all arrivals, and the potential for pax spending on high-margin shopping is usually very limited.
Surely the drivers do ferry operations between terminal and plane sufficiently often to be able to judge when they have 100 people on board their bus ?