Air travel can be stressful on its own, but toting beloved four-legged friends on board adds an extra level of responsibility and room for mishaps.

Two recent incidents involving United Airlines have left some animal lovers rattled: On Monday, a puppy placed inside an overhead compartment appeared to have suffocated, and the following day prompted United Airlines to investigate when a Kansas family’s dog was flown to Japan during a layover in Denver. The German shepherd, named Irgo, was reunited with his family Thursday night.

The Associated Press reported that last year, 18 animals, mostly dogs, died while being transported on United. This accounts for three-fourths of all animal deaths in cargo holds on U.S. carriers, according to the Department of Transportation.

“The vast majority — the overwhelming majority — of pets that travel with us have absolutely no problems whatsoever,” Charlie Hobart, spokesman for United Airlines told The Denver Post. “However, we understand completely how devastating it would be if a pet would pass away in our care, and we are doing everything we can to minimize that from happening again.”

On Thursday, United said it would begin issuing bright-colored bag tags to customers traveling with in-cabin pets.

As for the dog sent abroad, United released the following statement: “An error occurred during connections in Denver for two pets sent to the wrong destinations. We have notified our customers that their pets arrived safely and are on their way to be reunited with their owners. We apologize for this mistake and are following up with the vendor kennel where they were kept overnight to understand what happened.”

There are ways to take Fido along for the ride that can be less stressful for everyone involved, said Maia Brusseau, spokeswoman for the Denver Dumb Friends League.

First of all, if flying can be avoided, she said, that’s the safest and most comfortable option for any pet.

Brusseau also warned animals with flat faces, like pugs and bulldogs, can have a particularly difficult time breathing and may be more adversely affected by travel.

If travelers pursue bringing their pet on board the plane with them, Brusseau suggested calling the airline well in advance to find out what they require before a pet travels. Oftentimes, airlines require health certificates from veterinarians or vaccination records.

United requires pet owners to provide health certificates issued by a vet within 10 days of travel and proof of rabies vaccine for all dogs entering the United States, Hobart said. Animals who have been drugged are not accepted, nor are sick animals.

The service United uses to board flying pets, PetSafe, takes the pets to and from the aircraft in climate-controlled vans, Hobart said. The animals are the last loaded onto the aircraft and the first unloaded, he said.

Pets can also be tracked in an online itinerary by entering a number customers are given when they drop off their pets.

“They can look and see where their pet is all the time,” Hobart said.

Before boarding, Brusseau suggested playing with furry companions to tire them out for the trip.

United recommends owners give their pets honey or light Karo syrup for “carbohydrate loading” during the 24-hours before the flight to help keep up a puppy’s glucose levels, which if lowered can result in seizures and dropped body temperatures.

Hobart also recommended acclimatizing the animal to a crate weeks in advance and preparing the four-legged friend for air travel through simulations like driving through a car wash.

“If you have the option to drive instead of fly, that’s usually preferred,” Brusseau said.