Air traffic control sees through fog

On average, Auckland Airport is affected by fog six days a year. Photo / Kenny Rodger

New equipment which allows air traffic controllers to see exactly where aircraft are on the ground at Auckland Airport should cut disruption on foggy days.

The series of stations around the airport allow pinpointing to within less than a metre the position of aircraft and other vehicles fitted with transponders.

These transponders reply to signals transmitted from multilateration stations at fractionally different times by aircraft and these individual time differences allow an aircraft's position to be precisely calculated.

Airways NZ went through the final stages of commissioning the equipment last week and although it wasn't able to be used on Saturday, when about 25 flights were disrupted by fog, it should be in operation soon.

Airlines have stumped up $1.3 million for the system and Auckland Airport will soon be a leader in fog and severe weather technology in the Southern Hemisphere, said Airways' manager of main trunk services, Lew Jenkins.

Last year, another system known as Category III where a plane equipped with the right gear effectively auto lands in as little as zero visibility, was introduced.

Typically there are up to 45 aircraft movements an hour during the day at the airport but in fog this could drop around 12, even with the Category III equipment. With both systems there could be up to 20 movements an hour during severe weather, which can include heavy rain.

On average Auckland Airport is affected by fog six days a year although it has ranged up to 14 days.

Air New Zealand's chief pilot Dave Morgan said the technology would make life easier for everyone.

"Basically before you weren't allowed to leave the international apron until the other guy had parked up at the gate."

The airport company says not all airlines are Cat 111 qualified so some will still experience diversions. And because of the restriction in the number of movements in fog and priority for international flights there will still be restrictions to some domestic operations, especially smaller domestic regional services.

Airways is also installing multilateration equipment on hills around Queenstown to improve safety, but there it was aimed at locating planes in the air, rather than on the ground. The $2.5 million system involves 14 solar powered stations.

Mr Jenkins said Queenstown had grown from a small regional airfield to an international airport and the new system would enhance safety at what has been designated as a "black star" (critically deficient) airport by the International Federation of Airline Pilots.

Some airlines, including Jetstar do not yet have required navigation performance or RNP equipment and training, and this prevented them landing in Queenstown in poor conditions.

Mr Jenkins said that was an issue for airlines but his organisation's role was relatively simple.

"Our mantra is to keep them apart, keep them separated and prevent collisions."