NEW YORK (NYTIMES) - United Airlines apologised Tuesday (March 13) after a dog died on a flight during which it was stored in a passenger's overhead compartment.

A witness said a flight attendant had ordered the pet owner to put the dog in the compartment before the plane took off.

The dog, a French bulldog that was travelling in a pet carrier, was placed in the compartment shortly before United Flight 1284 left Houston for New York at around 6pm Monday, said Maggie Gremminger, 30, who was seated behind the pet owner.

She said the owner was instructed to put her dog there shortly after she boarded with two children, one of whom was an infant.

"The pet owner was very adamant that she did not want to put the pet carrier up above," Gremminger said. "She was saying verbally, 'My dog is in here, no, this is my dog.' The flight attendant, in response, really just continued to ask her to put it above because it was a hazard where it was, it was a safety emergency, someone could trip."

Eventually, the pet owner, whom United declined to name, complied with the flight attendant. Gremminger said the owner was preoccupied by her infant during the flight and did not check on the pet, which fell eerily silent after barking during takeoff and as the plane ascended to its cruising altitude.

Putting animals in the overhead compartment is against the airline's policies, which say pets are required to travel in carriers that "must fit completely under the seat in front of the customer and remain there at all times."

United said it was investigating who had put the dog in the overhead compartment and why.

"This was a tragic accident that should never have occurred, as pets should never be placed in the overhead bin," Maggie Schmerin, a spokeswoman for the airline, said in a statement. "We assume full responsibility for this tragedy and express our deepest condolences to the family and are committed to supporting them."