The Airline Pilot's Association says it is concerned Wellington airport's proposed runway extension is being done at the expense of safety.
The Wellington City Council and the airport are considering a 300 metre extension that will accommodate long-haul, twin-aisle jets.
New Zealand Airline Pilot's Association's (NZALPA) technical director David Reynolds said it was in favour of the runway extension, but was against the airport's current proposal to stick to the minimum safety requirements of a 90 metre Runway End Safety Area (RESA).
The RESA is a clear area at the end of a runway for planes to use to brake in emergency.
He said the airport needed to work toward the international best practice of a 240 metre safety zone, or the airport could install an area of crushable material, called an Engineered Materials Arresting System (EMAS), for a plane to sink into if it goes off the runway.
"It actually gives you an incredibly efficient way of slowing an aircraft down in a short distance," he said. "[Emas is] internationally approved and recognised as a scheme and it's one that we have ourselves put forward to Wellington airport as an alternative."
He said it was "down to cost".
"The airport essentially is building the runway to make more money," he said. "And what the airport is trying to do, like any other business, is to reduce its costs. What we're saying is, yes, that's great, reduce costs, but not when it comes to reducing safety margins."
According to the Civil Aviation Authority's rules, which adhere to international rules set by the International Civil Aviation Organisation, a RESA must extend to a distance of at least 90 metres from the end of the runway strip, and if practicable to a distance of at least 240 metres from the end of the runway strip.
Mr Reynolds said pilots had a vested interest in keeping passengers safe, because the pilot's safety was directly aligned with that of her passengers.
While NZALPA conceded that a 240 metre overrun zone, or an Emas, could be expensive, Mr Reynolds said "it's not there because it's economical... it's there essentially because it provides the correct level of safety."
In a statement, Wellington Airport said "the proposed extension and RESA requirements will be fully compliant with CAA regulations, which the current runway is also fully compliant with".