United Airlines is suspending new reservations for pets traveling in the cargo compartment after three dogs were loaded onto the wrong planes last week and a fourth died in an overhead bin.

United will honor reservations that have already been confirmed for PetSafe, its program for pets traveling in cargo, the airline said Tuesday. The suspension does not affect pets traveling with their owners in the cabin.

“We are conducting a thorough and systematic review of our program for pets that travel in the cargo compartment to make improvements that will ensure the best possible experience for our customers and their pets,” United spokeswoman Maggie Schmerin said in an emailed statement.

The airline said it would complete the review by May 1.

Chicago-based United diverted a plane to Akron, Ohio, on Thursday after discovering it had mistakenly loaded a dog aboard the flight from Newark, N.J., to St. Louis. Two days earlier, the airline sent a Kansas City, Mo.-bound German shepherd to Japan after switching it with a Great Dane.

All three pets have since been reunited with their owners, and all 33 people aboard the diverted flight were compensated, Schmerin said. The airline declined to estimate the cost of the compensation or the chartered flight that brought the dog home from Japan.

Those mistakes followed the death of a French bulldog that appeared to have suffocated after a flight attendant placed it in an overhead compartment on a three-hour flight from Houston to New York City earlier in the week.

Dog owner says United disregarded her pet’s barks for help before it died in overhead bin »

Amid the public outcry, two U.S. senators from Louisiana and Nevada introduced a bill that would ban stowing animals in overhead bins, and a New York state senator said she plans to introduce similar legislation that would also require climate control and ventilation for animals not traveling with their owners.

United already prohibits placing pets in overhead bins, but the airline said the flight attendant “did not hear or understand” the dog’s owner when she said there was a dog in the carrier. The airline said it took full responsibility for the bulldog’s death.

The bulldog was traveling in the cabin, not with the PetSafe program the airline is suspending, but United said it is also reviewing its service for in-cabin pets. The airline has already said it plans to issue brightly colored bag tags to better identify pets in carriers in the cabin starting in April.

United carried about 42 percent more animals in the cargo hold in 2017 than in 2015, and it accounted for about 27 percent of all animals U.S. airlines transported last year, according to the U.S. Department of Transportation.

It also reported an above-average number of animals that were injured, died or lost while in its custody. In 2017, 1.3 out of every 10,000 animals the carrier transported in cargo holds died, according to the Transportation Department, compared with 0.47 out of every 10,000 across all airlines that reported data.

As United has ramped up pet travel, American Airlines and Delta Air Lines have been cutting back. The number of animals the carriers flew declined 63 percent and 41 percent, respectively, between 2015 and 2017.

Delta said it introduced restrictions on pet travel during that period, including temperature limits and bans on snub-nosed breeds at a higher risk of health issues during air travel. American also restricts pet travel during extreme temperatures or for snub-nosed breeds and said it is not making changes to pet policies at this time.

United did not identify specific aspects of the PetSafe program it’s targeting for review but said it plans to work with independent experts in pet safety, comfort and travel.

The airline also said it will work with customers who want to cancel existing PetSafe reservations.

Susan Smith, the owner of Fort Lauderdale, Fla.-based Pet Travel, said she hopes United considers any options that would minimize risks to pets, but she also worries about the airline erring too far on the side of caution. Passengers with pets too big to travel in the cabin — especially those moving long distances, not just vacationing — don’t always have many options, particularly in summer, when some airlines are more restrictive, she said.

United uses climate-controlled vehicles to move pets from the airport to the plane and minimize exposure to hot or cold temperatures.

“We understand they need to review their program, but it would make it far more difficult if they decide not to continue,” she said.

Derek Huntington, president of the International Pet and Animal Transportation Association, said he’s worried about the impact of United’s decision to halt new bookings. The association represents companies that ship pets and other animals.

“What’s going to happen to those families that need to get from point A to point B when United might be the only option based on their location or the temperature restrictions airlines can impose?” Huntington said. “We don’t want this to be a permanent thing.”

While flying with a pet can be a challenge, there are steps owners can take to protect their pet’s health, including consulting a veterinarian before making travel arrangements, said Tracey Maione, president of the Chicago Veterinary Medical Association.

Sedating pets traveling in the cargo hold can be risky, but there are other medications, supplements and collars that can ease anxiety issues. Pets that get anxious in the car or during long trips could even be better off flying, said Maione, who is also the medical director of Oz Animal Hospital in Chicago’s Lincoln Park neighborhood.

She advised giving the pet time to get used to a carrier big enough to stand up and turn around in and timing flights during the coolest part of the day in summer and warmest part of the day in winter. Travelers should also mark pet carriers with a sticker indicating an animal is inside if the pet is traveling in cargo and let airline employees know about their pet if bringing it in the cabin.

“(Flying with pets) has been done for a long time, and it’s definitely doable, but there are certain safety steps and discussions that need to be handled first,” Maione said.

lzumbach@chicagotribune.com