Staffing levels of air traffic controllers are a "significant safety concern" and represents an increased risk to the traveling public, a union says.

An average of 5.6 flights are disrupted annually by controllers arriving late for work according to Airways data obtained by the Herald under the Official Information Act.

The union representing air traffic controllers, New Zealand Air Line Pilots Association (NZALPA), says the numbers represent ongoing concerns over short-staffing.

It comes after Police Minister Stuart Nash blasted one controller as a ''clown'' for turning up late to work and delaying his flight.

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"Air NZ Plane late leaving Napier by 20 minutes yet again; but for the 2nd Monday in a row it's because air traffic controller turned up late for work," he tweeted in September.

"Yet again a plane full of punters delayed because some clown slept in! Unbelievable & unacceptable."

Airways, which runs the air traffic system, said the delay was in fact caused by an air controller's car breaking down.

The new Airways statistics also show that illness accounts for around three flight disruptions every year, with a total of nine flights upset since 2016.

Over the same period, 17 flights were disrupted by lateness.

There are about 350 controllers throughout the country spread over 21 locations, with most in Airways' Christchurch radar centre and Auckland Oceanic centre.

Airways has previously said it runs at 99.8 per cent service availability across the network, which includes 17 air traffic control towers.

"Any unexpected drop in service is regrettable," said Airways' general manager air traffic services Tim Boyle.

"The level of service we provide at each of our locations is determined by legislation and is agreed with airlines and airports to balance safety, their operational and scheduling requirements and the costs of delivering the service.

"On occasions where our service is disrupted, airlines are able to continue to safely fly scheduled services under CAA-approved contingency airspace procedures."

But NZALPA says that while some locations are better than others, staffing needs reviewing to ensure air traffic controllers are "properly resourced and not operating under increased pressure created by staff shortages".

"The obtained data … represents a widespread and ongoing staffing issue that NZALPA has been aware is extremely frustrating for our members who are working very hard and just want to provide a safe and reliable service," a spokeswoman said.

"Our members, including our pilots, want to see the safety of the system put before profits, the dividend to the Government and refunds to airline customers."

Airways is investigating using remote' digital towers control traffic in some regional centres.

Controllers at central locations would be able to monitor the airfield by video and tracking systems.

The state-owned enterprise has already said the new tower in Wellington is among the last of the big traditional towers it would build.

Boyle told the Herald that Airways is in negotiations with a provider to develop a digital tower at Invercargill and a "contingency solution" for Auckland.

"Digital towers would provide a greater level of resilience and working from a centralised hub would make it easier to extend services if we needed to," he said.

"Our primary motivation around implementing this technology is to enhance safety and alleviate the concerns around disruption of services."