The goal is to avoid having to find a seat for a crew member after all passengers have already boarded.
United Airlines is now under vast scrutiny after a video of a passenger being dragged, bloodied and screaming, off a flight on Sunday went viral.
A total of 18,242 passengers were not allowed to board aircraft between April 2016 and February 2017.
According to Kanu Gohain, former Director General, DGCA, "A passenger could be denied boarding primarily for three reasons".
Ultimately, though, overbooking is done because airlines want to ensure that they are making the most money on every seat.
All passengers on United Express flight 3411 will be compensated equal to the cost of their tickets and could take the compensation in cash, travel credits or miles, United said this week. It also appears that the flight in question was not overbooked, just full. The DGCA, too, approves the practice.
UA staff and crew members who commute via the airline will now be required to check in 60 minutes prior to departure to prevent a repetition of the April 9 incident. Industry officials say that it is necessary because some passengers don't show up, and that overbooking keeps fares down by reducing the number of empty seats.
The DGCA, in its Civil Aviation Requirements (CAR), lays down a two-step procedure that airlines must follow in such circumstances. United reportedly asked passengers to willingly give up their seats in exchange for an airline voucher. Preferences were more evenly split among those who hadn't heard about the airline lately, with 51% choosing American. "They had nothing, none of their stuff", added Demetrio.
A passenger who rejects an alternate flight is also eligible for the same remuneration.
David Dao, the doctor who was videotaped being dragged by police officers, has filed an emergency court request for the airline to preserve evidence, signalling that he would fight back the case in court.
Overselling flights is a fact of life in the airline business.
The airline needed seats so that it could reposition crew, according to a statement from United.