Passenger numbers at Dublin Airport will be 34 million next year and to rise to 38.1 million in 2024, according to a projection by the Commission for Aviation Regulation (CAR).
That's based on a fairly modest growth rate of 3pc per year, but would put the airport dramatically in breach of current planning rules.
Passenger numbers are capped at 32 million a year, a condition of planning permission secured in 2006 for the construction of Terminal 2.
The cap was imposed because of pressure on infrastructure such as roads associated with numbers travelling in and out of the airport.
However, CAR forecast the much higher numbers through the airport as part of a review published last week along with its ruling on maximum passenger charges that can be levied by Dublin Airport for the next five years.
CAR cut the amount the airport can charge airlines per customer, but determined the amounts raised would still secure sufficient revenue to cover the cost of a €2.3bn capital programme.
The CAR determination appears to be based on levying the charges on higher passenger numbers than are permitted.
Last month DAA, which operates Dublin Airport, formally asked Fingal County Council - the local planning authority - to raise the cap on passenger traffic to 35 million.
DAA has also recently requested that transfer passengers - almost two million of whom flew into Dublin last year for connecting flights but never leave the airport - be excluded from the tally.
But based on CAR estimates even that won't keep pace with growth.