Originally Posted by
prestonh
Once legally boarded airlines have to remove 'with cause'. The Dr.'s conditions for removal did not fall under any of the conditions under "Refusal of Transport” (Rule 21) which were the only ones available that they could legally break the Dr.'s contract for the seat he possessed. The IDB order was illegal. The VDB was a negotiation but the pax held all of the cards since they were already legally boarded. Since we have not seen any force majeure declaration as you imply (pictures or it didn't happen) all we saw was force applied.
Force majeure = "unforeseeable circumstances that prevent someone from fulfilling a contract", "an event or effect that cannot be reasonably anticipated or controlled", "an unexpected event [...] which prevents someone from doing something that is written in a legal agreement". Totally legal as long as the airline proves it, which they should do bringing up schedules and flight records from the relevant flights (UA4680 GJT-DEN, UA4600 DEN-SDF, UA3411 ORD-SDF, UA4766 SDF-DEN) so the timeline of events make it clear the sudden crew requirement was unforeseeable.