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The appointment, a late addition to the agenda for the council's meeting on October 24, means Mr Boult will exercise the council's rights as the company's 75.1% shareholder for the next three years.
It drew criticism from members of lobby group We Love Wakatipu at the public forum of Thursday's council meeting.
Cath Gilmour told councillors they should revoke the "unfettered, three-year proxy", while Sally Stockdale said it was "curious" Mr Boult had been appointed for the entire council term.
However, Mr Boult told the Otago Daily Times the appointment simply made him the "appointed person to talk to the airport's board", and he had fulfilled the same role in his first term.
"Whether I was ever given a formal proxy to do that, I don't know, but in practice that's the way it worked."
His predecessor, Vanessa van Uden, had attended the board's meetings during her tenure.
"So I think you'll find it's just normal practice."
He did not attend the board's meetings to "give them my view of the world".
"All matters are discussed with council before I would ever go and vote on something, or give them any form of direction.
"It ignores the fact that we are an inclusive council, and I would simply not do that without discussing matters with the council beforehand."
He understood his appointment as proxy was a late addition to the October 24 meeting because the matter was "overlooked" until after the agenda was made public.
It had to be dealt with urgently because the airport's board was holding its annual meeting the next day, and the council needed to accept the company's annual report.
In her report for councillors on October 24, general counsel Alice Balme recommended the office of the mayor be appointed proxy, "as it has been historically", for the duration of the council's term.
The meeting's minutes state Ms Balme confirmed the proxy vote was "traditionally held by the office of the mayor".