Good dog or bad dog?

Delta Air Lines will soon require owners of service and support animals to provide more information before their animal can fly in the passenger cabin — including an assurance that it’s trained to behave itself.

The airline says complaints about animals biting other passengers or urinating or defecating on planes have nearly doubled since 2016.

Delta’s new rules are aimed at two categories: service animals, which receive specific training to help blind or disabled passengers; and so-called emotional-support animals, which require no training at all.

Neither is required to be caged during flights, and both fly for free.

The emotional-support group has been growing rapidly, and it is the target of most of the new Delta procedures. Delta — the second-biggest U.S. airline by revenue — said it transports about 700 service and support animals every day, nearly 250,000 per year. More than two-thirds are emotional-support animals.

That tally does not include pets, whose owners pay a fee to keep their carriers under their seat.

A rift has grown between people who rely on trained service animals and passengers with support or comfort animals. Many in the first group suspect that those in the latter are just trying to avoid having to pay to fly their pets.

However, owners of comfort animals — including veterans suffering from post-traumatic stress syndrome — often say that they wouldn’t be able to travel without their companion.

Abusing the system

Delta’s policy change arrives as the number of animals in cabins is on the rise — along with the number of problems.

Last June, a 70-pound dog flying as a support animal bit another passenger several times in the face on a Delta plane in Atlanta. The victim was hospitalized.

Eric Goldmann, a sales representative in Atlanta for a healthcare company, posts pictures on Twitter of support animals that he thinks should have stayed home. He says owners are abusing the system and creating safety hazards.

“These dogs are everywhere, they’re out in the aisles,” he said. “Planes have to be evacuated in 90 seconds in an emergency. If animals get in the way, people will panic.”

Although exact figures aren’t available, airline employees say dogs and cats are the most common animals on planes, but there have also been sightings of pigs, snakes and turkeys.

John Laughter, Delta’s senior vice president of safety and security, said there are insufficient rules in place to screen animals for health and behavior issues.

Delta is seeking a balance “that supports those customers with a legitimate need for these animals” while maintaining safety, Laughter said.

Sara Nelson, president of the largest flight attendants’ union, praised Delta’s decision. She said passengers abuse the system to bring untrained animals on board, and if it isn’t stopped it could lead to a crackdown that will hurt veterans and the disabled “who legitimately need to travel with these animals.”

Service v. emotional-support animals

Federal regulators have interpreted a 1986 access-to-travel law to mean that support animals must be allowed in airplane cabins and in apartment buildings that ban pets. That has created a cottage industry of online companies that help people establish their pet as an emotional-support animal.

Though airlines must allow support animals in the cabin, they can require owners to present a letter from a doctor or other medical provider who can vouch that having the animal there helps the human traveler. Delta will now ask to see those letters 48 hours in advance.

But airlines also complain that they have no way to verify that doctors who sign off on comfort animals are qualified to decide if someone needs the emotional support. Last year an undercover reporter for a Los Angeles TV station found a chiropractor willing to sign a letter allowing the woman’s dog to fly for free if she paid his $250 fee.

The Transportation Department — aided by an advisory committee of airline and passenger advocates — has been considering tightening the definitions of service and comfort animals. It missed its own deadline last year.

American Airlines and United Airlines said they were reviewing their animal policies. Both reported seeing a significant increase in the number of emotional-support animals since 2016.

Delta’s new rules

Starting March 1, Delta will require owners to show proof of their animal’s health or vaccinations at least 48 hours before a flight.

Owners of psychiatric service animals or those used for emotional support will need to sign a statement vouching that their animal can behave onboard.

But owners will be on the honor system — they won’t have to show, for example, that their dog graduated from obedience school.

In addition, Delta will now ask to see — 48 hours in advance — letters from a doctor or other medical provider who can vouch that the human traveler is helped by having the animal on the flight.

The new requirements don’t apply to pets, for which owners pay an extra fee — currently $125 each way for small pets in the cabin. Pets that don’t fit under a seat must fly in the cargo hold, also for a price. American and United have similar policies.