Ryanair and Aer Lingus are among the most complained about airlines in Europe, an investigation by The Irish Timeshas established.
The two airlines' rapid expansion has been matched by a steep rise in passenger complaints and court proceedings.
While Aer Lingus refuses to disclose the level of complaints it receives, and both airlines give no information on the outcomes of cases, information compiled from EU and Irish consumer groups and Irish aviation regulators indicates a growing level of customer dissatisfaction since new EU regulations protecting air passengers' rights were introduced over two years ago.
More complaints are made against Irish airlines than against carriers in 28 other European countries, according to figures from the European Consumer Centre (ECC) Network.
The centres are jointly funded by the European Commission and member states to provide help for consumers in cross-border disputes.
In 2005, 218 complaints were received about Irish airlines, virtually all relating to Aer Lingus or Ryanair, or more than one out of every six complaints made. Only the UK, with 207 complaints, came near the Irish total.
Since the figures were compiled, both airlines have introduced a number of charges, in particular for baggage, which have drawn further criticism from passengers.
Meanwhile, Ryanair is in the top five airlines for complaints received by the European Commission, a senior official in Brussels told The Irish Times.
This may not be unexpected given that Ryanair is one of Europe's biggest airlines. In 2006 it carried more passengers than any other European airline except Air France and Lufthansa.
The commission handles in total about 4,000 airline complaints a year.
Ryanair itself said it received more than 1,900 complaints in February but says this represented about one complaint per 2,000 customers.
The airline says 99 per cent of complaints were answered within seven days. Aer Lingus said it did not release figures on complaints.
Most air passenger complaints relate to flight delays, loss of or damage to luggage or cancellations.
Airlines are supposed to provide refreshments, meals and hotel accommodation in some cases of delayed and cancelled flights.
Compensation of up to €600 per passenger, re-routing and ticket refunds may also be required. However, in practice, many passengers find it difficult to secure their rights in such situations.
One in five cases handled by the Dublin office of the ECC now relates to air travel, compared to one in 20 in 2003.
In 2006, Ryanair was the subject of 266 complaints and queries to the ECC office in Dublin, a five-fold increase in two years. Some 109 complaints and queries were received about Aer Lingus, compared to 67 in 2004. The next highest number related to Iberia, at 56.
More than 93 per cent of cases were resolved in favour of air passengers, a spokeswoman said.
In Ireland, aggrieved passengers who are dissatisfied with the response of their airline are advised to contact the Commission for Aviation Regulation. It refuses to say how many complaints are received against individual airlines or to specify the outcome of complaints but a spokesman confirmed that it had handled more than 300 cases in the past two years. A further 200 cases were passed on to enforcement bodies in other European countries.
There is growing evidence that frustrated air passengers both in Ireland and abroad are using the legal system to get compensation.
Of almost 200 cases handled by the small claims court in Swords last year, more than 30 per cent related to the two big airlines, according to the local District Court.
Dublin airport, where both Ryanair and Aer Lingus are headquartered, lies within the area of jurisdiction of the court.