A global pilot union has warned pilots about flying into Auckland Airport, citing risk factors including an increase of broken runway slabs - some reportedly 30cm by 30cm and 12cm thick.

The warning comes after an emergency closure on Waitangi Day , the second runway incident in two weeks, resulting in multiple airline diversions and cancellations.

On January 24, two weeks prior to the Waitangi Day closures, a shutdown created chaos for travellers, with multiple flights rescheduled or delayed.​

Auckland Airport announced on Friday it would conduct an immediate review into the two unexpected runway closures.

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"While the two recent closures were unrelated, Auckland Airport recognises they have occurred in close succession with an impact on travellers and our airline partners," a spokesman said.

"The review will investigate these incidents to understand what occurred, and the speed of our response to reopen the runway on Waitangi Day."

The New Zealand Airline Pilots Association (NZALPA), said news of the runway debris was "extremely worrying".

Pool Auckland Airport closed its runway for emergency maintenance on Thursday, affecting thousands of passengers.

"Runway debris can cause a range of issues for aircraft, such as a punctured fuel tank or engine failure. We are dealing with a very serious situation here and one that the airport company has been aware of for a very long time," NZALPA President, Captain Andrew Ridling said.

"We can no longer stand aside and wait for the right thing to happen. We have moved past that point."

Ridling said the situation needed to be escalated "to whatever level is required to ensure something is done to resolve this situation, including Government intervention".

"If this issue is not dealt with, it has the potential to have far greater impact on the airport and the country than the damage to the fuel pipeline that affected the airport in 2017."

The International Federation of Air Line Pilots' Associations (IFALPA), a global pilots union, put out a safety bulletin on February 6, warning pilots flying into Auckland.

"The Auckland Airport runway has been deteriorating over the past few years," the bulletin said.

"The maintenance required to keep the runway surface in a usable condition has increased significantly, however, this has not kept up with the rate at which the runway is deteriorating."

Its "deteriorating" runway and the fact there was no alternative "increases the risk" when flying to Auckland, it said.



"This means there is no contingency when the runway is closed at short notice for any reason. This increases the risk when flying to Auckland and not carrying an alternate," it said.

The advice to pilots was to be aware of unplanned closures and to consider carrying extra holding fuel for arrival, the bulletin stated.

Auckland Airport said it conducted a physical inspection of the runway four times in every 24-hour period, as a part of its management programme.

It also carries out twice-weekly runway closures for planned and preventive maintenance.

However, the airport will temporarily close the runway outside these planned windows to closer inspect particular areas, to remove debris and/or to undertake maintenance if required.

Since the start of 2018, there have been four runway closures of more than 15 minutes due to runway maintenance, with an impact on scheduled flights.

A number of other unrelated issues may cause the runway to temporarily close, such as aircraft emergencies, wildlife or rubbish or debris.

The airport apologised for the number of flights that were diverted or delayed yesterday, which caused inconvenience to many travellers.

Auckland Airport said it was planning large scale repair works for the runway, including the replacement of concrete slabs near two touchdown zones.

"There is a current programme of planned maintenance for the runway, which includes an annual slab replacement programme," a spokesman said.

"Our review will also assess whether or not this programme of work should be adjusted."

The review will be completed in the next three weeks.

Ridling welcomed the airport's review of the closures, but said a three-week delay before review results were known was concerning.

"We can't let this be about funding, or stop to argue whether the airport company has properly prioritised runway planning and maintenance. We have to deal with the here and now and get this very serious problem addressed immediately."