Ryanair has attacked rival Aer Lingus for its fuel surcharges and management strategy after Ireland's national carrier revealed a first half loss last week.
Budget airline Ryanair is Aer Lingus' largest stakeholder with a 30 per cent share. Ryanair attempted to take over its rival last year but was blocked by the European Commission over competition concerns.
Ryanair said it is "deeply concerned" that Aer Lingus appears to be forecasting a loss of some 70 million (£56.7 million) in the current year.
Ryanair's spokesman, Stephen McNamara, said: "These half year results from Aer Lingus conclusively supports Ryanair's belief that its 2006 takeover strategy for Aer Lingus was the right one.
"As the current wave of European airline mergers and takeovers gathers pace, it is clear that Aer Lingus is being marginalised on the sidelines of European aviation, losing money, with no apparent strategy to return to profitability.
"Its independence strategy, which over the past year has delivered higher fares, a sixfold increase in its fuel surcharges, route closures in Ireland, and a lurch to substantial losses has failed its customers, its staff and has we believe failed to secure Aer Lingus's long-term viability."
Aer Lingus should scrap its "unjustified" fuel surcharges which are losing the airline business, recognise that it has failed to keep down costs and pay its board members less, the airline said.
In its first-half results, Aer Lingus blamed soaring fuel prices for the loss and a consumer slowdown for an operating loss of 22.3 million (£18 million).
The results make the carrier a takeover target, as the industry begins a process of consolidation.