1. Federal law allows United Airlines -- and other air carriers -- to routinely overbook flights. This practice ensures that flights are full, or nearly so, maximizing airline profits.
2. If more passengers show up than there are available seats, the airline can ask for volunteers to be bumped to a later flight.
3. Bumping can also occur when an airline needs to transport employees needed on flights elsewhere.
4. Correction: Flight 3411 was not overbooked, as many outlets have reported. United simply needed the seats for four of its employees who were scheduled to work on flights originating from Louisville the next day.
5. United first offered the passengers $400, then $800. By law, United could have increased its offer by another $550, but did not.
6. In exchange for being bumped, passengers may receive a flight voucher worth up to $1350 and a hotel room, if they'll be delayed more than four hours.
7. Flight vouchers often carry numerous restrictions and blackout dates, making them difficult to use later and therefore, worth less.
8. Bumps typically happen before passengers are allowed to board the plane.
9. If not enough passengers volunteer to be bumped, United -- like other air carriers -- will select passengers for a later flight.
10. Passengers are not selected at random, but by a system that takes into account a passenger's age and any disability, the ticket price paid, their check-in time, frequent flier status and flight class.
11. This practice is buried in the small print of the carrier contract, which each passenger agrees to -- but rarely reads -- upon purchase of their tickets.
12. On Sunday night, April 9, at Chicago's O'Hare Airport, United required four seats on a sold-out flight to Louisville.
13. Passengers had already been seated when the request for volunteers was made.
14. The seats were required for United employees needed on flights leaving from Louisville.
15. United should have known those four seats were needed before -- not after -- passengers had boarded.
16. None of the seated passengers volunteered, so United selected four passengers using its age/disability/price/check-in/status/class formula.
17. Two of the selected passengers left without complaint. One left under duress. The fourth refused to give up his seat.
18. The fourth passenger was a 69-year-old doctor from Louisville, who said he needed to be at the hospital the next morning in order to see patients.
19. Update: The fourth passenger has been identified as Dr. David Dao, of Elizabethtown, Kentucky.
20. Update: Dr. Dao's medical license was suspended in 2005 following multiple convictions in a sex-for-prescription-drugs case involving one of his patients; it was provisionally reinstated in 2015.
21. United called for assistance from the Chicago Police Department and airport security.
22. Two Chicago police and an airport security officer in street clothes boarded the plane. The security officer forcibly removed the fourth passenger.
23. Update: The non-uniformed officer has been placed on probationary leave.
24. At least two other passengers recorded the incident on their phones, and later posted the videos to social media.
25. The videos show the passenger screaming, being removed from his seat, and dragged up the aisle, his mouth bloodied.
26. Several passengers can be heard protesting the passenger's treatment, though none moved to stop the passenger from being removed or volunteered to give up their seat for him.
27. Other passengers are shown doing their best to ignore the situation.
28. A later video shows the man re-entering the plane and running back toward his seat. He appears visibly disoriented, repeating, "I have to go home."
29. Yet another video shows the man at the cabin entrance, blood now streaked across the lower half of his face. In this one he repeats, "I have to go home. Kill me now."
30. A number of news outlets reported the incident on Monday morning, and the videos began going viral on social media.
31. Also on Monday morning, the CEO of United Airlines, Oscar Munoz, released a statement apologizing for the need to "re-accommodate" these passengers, and stating that the airline was "reaching out to this passenger to talk directly to him and further address and resolve this situation."
32. Update: Ironically, Munoz was named PR Week's "Communicator of the Year" this past March, 17.
33. Update: After his first statement was criticized and an internal memo released in which Munoz stated that he stood behind United's employees, he made a second, more sincere apology to Dao and the flight's other passengers. In it, he promises an examination of United's policies with a report to come on April 30.
34. Update: A second story has emerged of a United flight from Hawaii to Los Angeles. The first-class, full-fare passenger was told to give up seat in favor of a higher-priority passenger, and threatened with handcuffs if he didn't agree to move.
35. Since 2010, United, American, Delta and Southwest have earned more than $20 billion in profits annually, and own 80 percent of seats on domestic flights.
36. Passengers who find themselves in a similar situation have little recourse. According to The Atlantic, "In the last decade, class-action lawsuits have become endangered thanks to a series of Supreme Court rulings that have undercut consumer rights. Disputes over fine-print regulation are increasingly likely to be settled in arbitration, without a judge or jury, where the deck is stacked against the individual plaintiff and the decisions are practically impossible to appeal."
37. Neil Gorsuch, formerly a justice for the United States Court of Appeals Tenth Circuit, has a record of siding with corporate interests over consumer rights in similar cases. He was confirmed as an associate justice of the United States Supreme Court today, Monday, April 10, 2017.