Ryanair will formally ask the Commission for Aviation Regulation to change the way Dublin airport allocates take-off and landing slots in light of a new consultancy report, the High Court heard yesterday.

The private airline wants the commission to reverse its decision of February this year which changed the allocation of slots from "schedule facilitated" to "co-ordinated" and also changed the control system for take-off and landing.

Under the co-ordinated designation at Dublin airport, airlines do not have an input into the control of operating slots for take-off and landing. Instead, a schedules facilitator appointed by the Commission - Airport Co-ordination Ltd (ACL) - decides on the allocation of slots.

If the commission does not change back the designation of the airport, the airline may consider bringing another separate legal challenge, Bill Shipsey SC, for Ryanair, said yesterday.

Ryanair had initiated proceedings challenging the slots decision but Mr Shipsey asked that the challenge be adjourned as a new consultancy report on the airport was considered.

He said the case related to the allocation of take-off and landing slots and runway capacity. He said in one consultants' report on capacity, relied upon by the commission when making its decision, the assumption was made that the maximum number of take-offs and landings at peak time was 31 per hour.

However, another set of consultants had published a report in May last on the implications of a second terminal at Dublin airport. That report appeared to be operating on the assumption peak time take-offs and landings were in the region of 36 to 38 per hour.

Counsel said the information on which both reports were based was provided by the Dublin Airport Authority and was inconsistent. Ryanair's solicitors had written to the commission, asking it to explain the "discrepancy" and to return the airport to "co-ordinated" status.

Mr Shipsey asked that the current challenge be adjourned. Mr Justice Roderick Murphy agreed to the adjournment on the basis Ryanair would bear the costs.

The Dublin airport summer slots schedule which was included in the Ryanair challenge will not now be affected by the case as it will not come before the courts until at least October.

The challenge was initiated after the commission, in decisions of February 12th and 13th last, decided to alter the designation of Dublin airport from schedule-facilitated to co-ordinated for summer and winter 2007 with regard to the allocation of slots.

In its decisions, the commission said it had concluded, following consideration of a report by Jacobs Consultancy, that it was necessary to alter the airport's designation because the capacity problems at Dublin airport would be such as to produce "significant delays" from summer 2007, which could not be resolved in the short term.

A schedules-facilitated regime, according to Ryanair, offers airlines greater flexibility in scheduling their flights and ensures that airport managers operate their airports "with a constant eye of ever-greater efficiency and with due regard to the benefits of competition".