Safety at Wellington airport is in dispute with the director of Civil Aviation saying it is safe and the pilots’ union saying the risk of an overrun or undershoot is significant.

The airport company wants to extend the length of the runway and Civil Aviation director Graeme Harris has accepted, for now at least, that a longer runway would not mean longer safety zones.

The issue has erupted in the midst of a pilots’ claim that Harris has mistaken the way he should interpret the law about the length of the safety zones.

Harris says Wellington airport is safe with 90m safety zones and, based on current information, 90m would be acceptable on a longer runway also.

The New Zealand Air Line Pilots’ Association, representing 1600 pilots and 400 air traffic controllers, said the law required 240m zones at each end of a runway like Wellington, if practicable. The airport company said that could cost more than $280 million.

Much of a hearing at the High Court in Wellington centred on the meaning of “practicable” and the factors relevant to deciding what was practicable.

The pilots’ lawyer, Hugh Rennie, QC, said it was the pilots and air traffic controllers who had the responsibility of operating safely at the flight level.

The union took the court action because the approval, cross checks and responsibility system Harris relied on was not working.

The pilots and air traffic controllers had “deep concern” they had not been involved and consulted, and that valid decisions were not made.

Justice Karen Clark reserved her decision. She said it was unlikely to be delivered this year.

The airport company has yet to apply for resource consent for a 350m extension at the southern end of the runway jutting into Lyall Bay.

Rennie said Harris preferred to allocate the extra length to runway rather than the end safety zones, but he had no power to do that.

The union, Harris, and the airport company disagree about the level of consultation with the union.

Harris also says he has not made a decision about the safety zones. He says he has expressed a “view”, a term the airport company lawyer Victoria Heine called “a little cute”. Rennie said Harris needed to be saved from himself.

Harris’ lawyer, Francis Cooke, QC, said the airport was safe and met international standards with the 90m safety areas.

Wellington had been assessed against international standards and it was seen as very low risk in terms of safety, Cooke said.

The minimal improvement from extending the safety zones had to be balanced against the high cost of engineering and reclamation.

Based on international data the prospect was “extremely low” of overruns or undershoots at Wellington airport for the larger planes the airport was hoping to attract with a longer runway, Cooke said.

But Rennie said it was not possible to take general data that incorporated many factual differences and use it to predict the probability of a rare event at a single location.

Expert local pilots said the probability at Wellington was significant,  Rennie said.

Heine said it was calculated that increasing the safety zones from 90m to 140m or 240m would give marginal improvement and did not outweigh the cost. The recommendation was that it was safe now and it would be in future.