A public inquiry into controversial plans to scrap a cap on passenger numbers at George Best Belfast City Airport has heard how the limit on seat sales is an effective way of controlling aircraft noise.
Under the current planning agreement, no more than two million departure seats per year can be sold from the airport under the Seats for Sale scheme.
But George Best Belfast City Airport wants to abandon the scheme, claiming it's hampering economic development both at the airport and in Northern Ireland.
East Belfast residents and Belfast International Airport are opposing the bid to remove the cap, which is the only one of its type in the UK, claiming noise levels from flights would become intolerable.
A lawyer for Belfast International Airport told the inquiry at the Planning Appeals Commission in Belfast yesterday that the current Seats for Sale scheme was an effective noise control as it indirectly affected the size of aircraft operating in and out of the airport.
He said there was a correlation between the size of aircraft and noise levels and that the Department of the Environment "got it right" when the scheme was introduced.
A legal representative for Belfast City Airport Watch - made up of residents' groups opposed to the removal of the Seats for Sale cap - told the inquiry that the scheme worked perfectly well.
However, Mark Beattie, operations director at George Best Belfast City Airport, said that the seats limit was not an effective restriction on flight numbers and noise.
A lawyer for the airport also told the inquiry that the scheme gives "no credit" to newer types of aircraft which have more seats but are quieter than older variants.
The Department of the Environment told the inquiry it was neutral to whatever outcome emerges but held the view that noise restrictions would be a more effective control than Seats for Sale.
In 2010, then Environment Minister Edwin Poots ordered the removal of the cap, a decision that has been legally challenged three times.
The public inquiry, ordered by former Environment Minister Alex Attwood in 2011, is due to last until Thursday.
It is expected to hear evidence from a wide range of parties including airport officials, residents and aircraft noise experts.
Before yesterday's hearing Dr Liz Fawcett, chair of the Belfast City Airport Watch steering group, said the airport's plans were unacceptable.
"We have robust evidence that many residents and their children already suffer disrupted sleep, higher stress and poorer quality of life, due to existing levels of aircraft noise," she said.