Work was beginning on Monday on a replacement for a runway lights cable at Auckland International Airport that failed on Saturday, disrupting travel plans of hundreds of passengers.
Twenty-two flights in and out of the city had to be diverted or delayed after the lights failed about 8.10pm on Saturday because of a cable fault.
About 2000 people had their travel plans disrupted, with hundreds spending an uncomfortable night camping at Auckland, Wellington and Christchurch airports.
After exhaustive testing, airport operations were fully restored at 5.30am on Sunday.
While the backlog was cleared at domestic terminals, some passengers were still stranded in Los Angeles on Sunday night.
Technicians made temporary repairs on Sunday and were to work on a permanent replacement on Monday.
The Airways Corporation, which is responsible for the lights, says a formal investigation is underway to establish the cause of the failure and identify any other cables at risk.
The company did not on Monday know the specific cause of the problem, but technicians had removed the faulty section of cable to try to find out.
Operations manager Lew Jenkins says the agency is also studying cable plans to see whether there are other vulnerable points.
He said the company alerted airlines as soon as it was aware of the problem at the weekend and is not to blame for any delay in letting passengers know.
Mr Jenkins says there will be discussions about potential compensation for passengers this week.