Passengers who reach boarding gates after the aircraft door is closed wonder why they were not allowed to board. After all (as the perception is), it would not take long for a mere door to be opened to let a person enter the plane. But boarding an aircraft is not like boarding a train: Aircraft doors close by protocol about 15 minutes before departure. And there are good reasons for this:

A weighty matter
It’s all about weight distribution

When the captain and co-pilot walk into the aircraft, a flight dispatcher gives them the expected weight on board:
-Fuel weight + cargo weight + passengers’ weight
-Information on the total number of passengers is not given at the time
-The pilot starts feeding the weight data into the flight management computer. Among other things, it calculates various speeds, such as different speeds for take-off and approach
-The technical log comes in and it gives more weight details, such as tons of fuel and litres of oil in engines
The next steps
After the final check-in bag is put into the hold, the last piece of cargo loaded and the last passenger has boarded, a ground staff member comes to the commander and hands him/her a set of papers called load and trim sheet.
This sheet lists details such as:
Final number of passengers and crew on board
-Break-up of male, female, infants
-Weights loaded onto each zone of the aircraft
-Whether aircraft is loaded in such a way that its center of gravity remains within prescribed zone through all stages of flight
The aircraft door is shut
-Cabin crew certify that all passengers are seated with seat belts on before pushback
-Crew ensure that all aircraft doors are armed (setting door to automatic mode so that emergency evacuation slides will deploy if opened)
-The aircraft is now ready to push back
Last steps
-Pilots inform ATC about he total number of people on board and seek clearance for push back. Eg: “XYZ 124, we have 180 people on board. Ready to start up and taxi. ” ATC will either give clearance or inform pilot that they are number x in sequence/queue
-At this point, if aircraft door has to be opened to accommodate even one passenger, the entire process has to be repeated!
-The moment the aircraft parking brakes are released, the departure time is registered electronically





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