When the passenger is barefoot.
When the passenger appears to be intoxicated or under the influence of drugs.
When a passenger attempts to interfere with the flight crew or fails to obey their instructions.
If a passenger has a contagious disease that might be transmissible to others during flight.
When the passenger has “a malodorous condition.”
When the passenger is unable to sit in a seat with the seat belt fastened.
When the passenger’s conduct creates an unreasonable risk of offense or annoyance to other passengers.
According to Delta’s terms, passengers won’t be entitled to compensation if they are denied boarding if the traveler hasn’t complied with the Delta’s contract of carriage.
It stipulates that the carrier can remove any passenger for “unforeseeable conditions” including as a result of weather, acts of God, strikes, etc.
Also, passengers can be taken off the plane if they “cause a disturbance such that the captain or member of the cockpit crew must leave the cockpit in order to attend to the disturbance.”
Among other reasons listed by United for removing passengers from flights:
Passengers in their ninth month of pregnancy who don’t have a recent doctor’s note clearing them for travel.
Not following the airline’s policy on smoking or use of smokeless products.
Being “unable to sit in a single seat with the seat belt properly secured, and/or are unable to put the seat’s armrests down when seated and remain seated with the armrest down for the entirety of the flight, and/or passengers who significantly encroach upon the adjoining passenger’s seat.”
Those “unwilling to follow UA’s policy that prohibits voice calls after the aircraft doors have closed, while taxiing in preparation for takeoff, or while airborne.”
United’s contract also says passengers agree that if they engage in any of the listed activity and incur expenses for the carrier, they agree to reimburse the airline for those costs.