Passengers reportedly heard the dog barking throughout the flight, but after landing discovered that the animal died at some point during the trip.
United has taken responsibility for the incident and released the following statement to The Points Guy: “This was a tragic accident that should never have occurred, as pets should never be placed in the overhead bin. We assume full responsibility for this tragedy and express our deepest condolences to the family and are committed to supporting them. We are thoroughly investigating what occurred to prevent this from ever happening again.”
According to the policy on United's website: "A pet traveling in cabin must be carried in an approved hard-sided or soft-sided kennel. The kennel must fit completely under the seat in front of the customer and remain there at all times... A customer traveling with an in-cabin pet cannot be seated in the bulkhead or an emergency exit row."
Overhead bins are not designed to circulate air, and it's possible that played a role in the animal's death. No official cause of death has been released, however, and the flight crew member's reasons for insisting it be kept in the overhead bin are unknown.