Pilots would have lost all radar communication during an outage that grounded hundreds of flights on Tuesday.



Flights across the country have gradually resumed after fault, which affected the entire country.



At 2:41pm on Tuesday, an "internal network failure" caused all flights to be grounded until about 4pm.



The New Zealand Air Line Pilots' Association spokeswoman Lisa Williams said pilots flying at the time of the fault would have lost all radar communication.



Pilots would have consulted an emergency procedure manual or aeronautical information publication contained in all cockpits, she said.



Air traffic control would still have been able to communicate with pilots via radio, she said.



"It is an extremely rare event," she said.



READ MORE: Investigation into radar failure



Were you affected by the outage? Email us photos and information to newstips@stuff.co.nz



Airways Corporation, which manages the radar system, said it had now identified the issue and "thoroughly tested the integrity of the system".

"At no point was the safety of any airport operations compromised," the company said in a statement.

"Airways apologises to all passengers who have been affected by this outage. Our immediate priority is resolving the situation and we are unavailable for interviews at this stage."

LAWRENCE SMITH/Stuff.co.nz Flights were delayed in Auckland after a radar fault in Christchurch.

Airways said around 50 airborne flights had been directly affected by the fault.



"Throughout this outage we had back-up processes in place to deal with this eventuality safely," Airways said in a statement.



"We did not recommence departures until we were completely confident in the safety of all our systems."

After the problem was fixed, Auckland Airport tweeted that international flights would depart first with some delays expected.



Transport Minister Simon Bridges said: "I have been assured that at no time was the safety of passengers or planes compromised."



HUNDREDS OF FLIGHTS DELAYED

KEVIN STENT/Dominion Post Passengers in Wellington airport have been delayed after a national radar fault grounded airplanes.

Flights out of Auckland Airport were delayed



Air New Zealand said about 160 of its international and domestic flights were disrupted, with passengers likely to experience delays.



"Flights are now departing but the backlog will take some time to clear," the airline said.



Passengers were asked to check arrivals and departures information at www.airnz.co.nz for up to date information on flight departures.



Jetstar spokesman Phil Boeyen said about six domestic Jetstar flights had been impacted so far with the longest delay at this stage around 90 minutes.



He did not know the exact number of Jetstar passengers affected but said it would be several hundred over six flights.



Chris Yorke landed in Wellington nearly two hours late after his flight from Blenheim was held back during the radar failure.



"We were called to board but then told the boarding was cancelled," he said.



Yorke and his fellow passengers had to wait 1.5 hours but were lucky it was inside the terminal and not the plane, he said.

When the passengers were told the radar system was down most were understanding, he said.

"You don't want to be flying when the radar is not working. You'd rather be on the ground."

stuff.co.nz Flights across the country were grounded after a fault in the national radar system was discovered.

HORROR RUN



At Christchurch Airport, some flights to Invercargill and Dunedin had resumed by 5pm, but flights to New Plymouth and other towns were cancelled.



Passengers were told to go to reservation desks to arrange accommodation.



Erica and Nogs Karati said it was likely they would be stranded in Christchurch overnight.



The couple had a horror run since returning from Vanuatu at 2am on Tuesday.



They went to the wrong motel on arrival, had a couple of hours sleep, then flew from Auckland to Christchurch only to be told of delays.



Their car was waiting for them at Queenstown Airport, and they faced a couple of hours driving from there to get home to Invercargill - if the roads were clear of snow.

"There goes another couple hundred of dollars," Erica Karati said.

"I don't really think we should go on holidays any more."

An image from FlightRadar24.com shows New Zealand's air traffic at 4:37pm.

Two flights - to Auckland and Christchurch - had been cancelled and all others were delayed by at least an hour.

'THESE THINGS HAPPEN'

Dozens of passengers were stranded at Nelson Airport, many of them on mobile phones trying to make other arrangements or book new flights.



Sue Leov, of Nelson, was already on her flight to Auckland to meet her daughter, who she was travelling with to Phuket, Thailand, on Tuesday night, but was forced to disembark because of the radar fault.



"The plane was warming up and then they said, 'Sorry, you're going to have to get off the plane because of the radar'.



"I was a bit worried they were going to cancel our flight because they cancelled a whole lot of other ones."



Her flight was delayed for more than two hours, boarding shortly after 4:30pm.



Amber Watt and Arron Saunders were waiting with three-month-old daughter Lucy.



They were supposed to be leaving for Wellington at 3:30pm to stay with Watt's mother, but they were still grounded at 5pm.



"She's not leaving until she knows we're definitely not coming today.



She had been told that they should expect a one hour delay, but hadn't had any news by 5pm.



"I'm not too bothered, though. We've both travelled internationally, these things happen. I'd be disappointed if we didn't get out today.



"I'd be annoyed if we got here and it had been cancelled and we hadn't been told or it was something within the airline's control, but it's not so that's cool."

An image from FlightRadar24.com shows New Zealand's air traffic at 3:50pm.

It was to be Lucy's first ride in airplane, but she had fallen asleep in Saunders' arms, not bothered by the delay in the slightest.

'COMPUTER RESET'

Family First spokesman Bob McCoskrie was on a plane due to depart from Wellington to Auckland just before 3pm when passengers were notified of the problem.



"We got on the plane, the door closed and then there was no action," he said.



"We were told the computer was being reset because the radars were down and it might take 10 to 15 minutes."



Passengers were still sitting on the grounded plane at 3.40pm.



Jonathan Carson Passengers are delayed at Nelson Airport.

'NEVER HAPPENED BEFORE'

Heather Davis, from Motueka, arrived at Auckland Airport domestic terminal with her daughter and granddaughter at 3.30pm when the air traffic control outage was broadcast over loudspeakers.

Their 4.15pm flight to Nelson was cancelled and they were waiting to rebook.

An Air New Zealand staff member told them the radar outage had never happened before.

Davis said the delay was "slightly annoying, but obviously the air traffic control system is very important and we would rather they got it sorted, so we are happy to wait."