A dog died on a United Airlines flight when an attendant forced its owner to place it in the overhead cabin during the entire 3.5-hour journey.
US media reported lack of oxygen as the likely cause of death.
The carrier has taken full responsibility for the "tragic accident that should never have occurred."
"Pets should never be placed in the overhead bin," it added.
The incident happened on Houston-New York Flight 1284 on Monday. A woman was traveling with her children and dog.
Witnesses said an attendant came and asked her to put the small bag, which contained the dog, in the overhead cabin.
She adamantly resisted, but eventually complied.
"At the end of the flight, the woman found her dog, deceased," tweeted Maggie Gremminger, a co-passenger.
I want to help this woman and her daughter. They lost their dog because of an @united flight attendant. My heart is broken. pic.twitter.com/mjXYAhxsAq— MaggieGremminger (@MaggieGrem) March 13, 2018
I want to help this woman and her daughter. They lost their dog because of an @united flight attendant. My heart is broken. pic.twitter.com/mjXYAhxsAq
The attendant later claimed she didn't know the dog was in the bag, but United assumed responsibility.
"We are thoroughly investigating what occurred to prevent this from ever happening again," it said.
It has refunded the family the ticket cost, plus the $125 pet cabin fee.
With 18 deaths, United had the highest number of animal deaths among all US carriers in 2017.
Want to share it with your friends too?
Love World news?
Subscribe to stay updated.