Three new Aviation Security puppies in May 2016, including Grizz.

Firing a tranquiliser gun to stop a dog running loose on Auckland Airport tarmac was "implausible", an expert vet says.

Grizz, an Aviation Security dog, was shot early on Friday morning after escaping from his handlers.

His escape caused lengthy delays for more than a dozen flights.

Airport staff spent three hours trying to catch him without any success, and eventually asked police to shoot him so that flights could resume.

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His death has shocked commentators, including TVNZ's Hilary Barry, who suggested authorities should have tranquilised the dog instead of killing him.

But Callum Irvine, head of vet services at the New Zealand Veterinary Association, has poured cold water on those claims, saying they were unrealistic.

"There just isn't ready access to tranquiliser guns and darts in New Zealand, and even if authorities did manage to get their hands on one in time, there are so many other factors to take into consideration, like how close the animal is, the animal's weight, age, and how much adrenaline was also running through the body."

Irvine, a vet of 19 years, said although vets have access to sedative drugs as part of routine practice, most wouldn't carry tranquiliser darts or guns because there isn't usually much need for them.

"The bottom line is that probably no vet clinic in the country actually has or uses tranquiliser guns or darts anymore.

"The only place that you might see a tranquiliser gun used is in a wildlife park or in a zoo, and even then, very rarely - it's a fairly crude form of delivery of sedation."

He said guns and darts are designed for animals that are already enclosed, so the shooter would have to get quite close to the animal in order to hit it.

"We don't know the circumstances under which the dog was shot this morning - but the reality is that it administering sedative to an animal on the loose can be very difficult."

There was also no guarantee the animal was going to respond in a certain way.

"If it's not done right, a partially sedated animal can become even more distressed, and fearful and difficult to manage - and become even more of a danger to those around it."

Grizz's handler said he was "very upset" after the dog was shot dead.

Nicky Thorburn posted on Facebook, saying that his father was the Avsec handler in charge of Grizz at the time.

"It was a last resort, my dad is very upset about this," he said.

"I'm reading disgusting comments . . . and people need to understand how traumatising and upsetting this was for him.

"Please have compassion."

Thorburn said his father, Noel Thorburn, had worked in customs and aviation security for more than thirty years, and was considered one of the best at what he did.

Airport spokeswoman Lisa Mulitalo said Grizz was only killed as a last resort.

Embarrassed to be a kiwi today. Killing a dog so flights can continue Auckland Airport. No excuse! Disgusting #poordog #aucklandairport — juliette banks (@julzbanks) March 16, 2017

"They did everything they could, but unfortunately the dog had to be shot," she said.

"We're really upset about it."

Current status: Sitting in a plane in Tauranga that can't take off because a dog is on the Auckland Airport runway. — Adam Morris (@bigmarnmorris) March 16, 2017

Aviation security spokesman Mike Richards said Grizz had been on the loose for about three hours.

"At around 4.30am an Avsec security detector dog was spooked and got away from his handler," he said.

"The emergency operations centre was activated and a search was commenced."

Richards said 16 flights were delayed, as pilots would not risk passenger safety with a dog on the loose.

Inspector Tracy Phillips said airport staff eventually asked police to shoot Grizz about 7.30am.

"This followed considerable efforts over several hours by Avsec and airport staff to contain the dog," she said.

"This is not an outcome which anyone wanted, and police were only asked to be involved as a last resort."

Unfortunately an Aviation Security dog was shot this morn @AKL_Airport staff had tried for 3 hours to catch it our thoughts are with handler — Auckland Airport (@AKL_Airport) March 16, 2017

Richards said those involved understood why Grizz had to be killed.

"The handler and Avsec are naturally upset but do understand there were no other options, in the very difficult circumstances," he said.

Andrea Midgen, the acting national chief executive for the SPCA, said the airport would only have shot Grizz as a last resort.

"I would say it's one of those unfortunate accidents," she said.

"They put a huge investment in those dogs to do the job they do, and they treat them as part of the family."

Grizz was one of three puppies which joined the Avsec team in May 2016.

Avsec posted pictures of the trio at the time, but it wasn't immediately clear which of the dogs was Grizz.

Midgen said her thoughts were with aviation security staff as they had lost an important team member.

"It would have been the hardest decision they've had to make."

Richards said the focus in coming days would be on understanding what had gone wrong.

"Avsec will undertake a review of the incident to try and ascertain what spooked the dog, and if this has any implications for ongoing training," he said.

AVIATION SECURITY SERVICE (AVSEC) DOGS

Avsec's explosive detector dogs (EDD) have different jobs than the customs and MPI pups, tasked with sniffing out explosives rather than drugs or food.

Each EDD has a human partner, or handler, and they work together to ensure no dangerous materials are present in our airports or on aircraft. They're based in Auckland, Wellington, Christchurch and Queenstown.

The job requirements for an EDD are to be happy, confident, sociable, non-aggressive and love playing with toys. Avsec doesn't discriminate by breed.

Dog teams undergo 10 weeks of training before graduating from the Police Dog Training Centre as operational.

The dogs' presence in airports can deter potential explosive-layers and they also conduct random searches around the airport, such as at check-in counters, screening points and gate lounges.

They also back up police and customs and corrections teams when there are bomb threats.

Mobile and quick, the dog teams are considered the most reliable and cost-effective way of detecting explosives.

*An earlier version of this story incorrectly named the dog as Frizz, due to a spelling error by Avsec. The dog's name was Grizz.

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