Camera phone footage captured the heavy handed approach of security officers who dragged Dr Dao from his seat. He had two of his teeth knocked out, broke his nose and suffered concussion, according to his lawyer.

Now United says it will require employees seeking a seat to book it at least an hour before departure.

An internal memo, obtained by TMZ, said the change was so that seats could be made available before passengers had boarded the plane.

Had the rule been in place last Sunday, United Express Flight 3411 still would have been overbooked by four seats, but United employees could have dealt with the situation in the gate area of Chicago O’Hare airport instead of on the plane.