Ryanair accounts for 60 per cent of complaints made by passengers to the Irish aviation regulators, new figures show.
The airline is the subject of significantly more complaints about flight cancellations and delays than any other airline using Irish airports, according to the Commission for Aviation Regulation.
However, Aer Lingus tops the list for complaints by passengers who were denied boarding for their flights because of overbooking.
The high number of complaints against Ryanair is only partly explained by its size; last year Ryanair accounted for 36 per cent of passengers leaving Dublin airport and Aer Lingus accounted for 33 per cent.
In response to requests from The Irish Times, the regulators have for the first time provided details of the complaints received about individual airlines. These figures cover the first four months of this year but the commission said it plans to release statistics on a regular basis in future.
A spokesman was unable to say what the outcome of the cases were but he said that airlines provided aggrieved passengers with some form of compensation, such as a voucher or a refund, in a significant number of cases.
When passengers suffer long delays, have their flights cancelled or are denied boarding, they are usually entitled to compensation from the airline. Exceptions arise over problems outside the airline's control such as bad weather or strikes.
Passengers seeking compensation are advised to first take up the matter with the airline. However, Aer Lingus refuses to provide any information on the complaints it receives, while Ryanair said it receives less than one complaint per 1,000 passengers.
If passengers are dissatisfied with the airline's response, they are advised to contact the commission.
So far this year 135 passengers have taken this step and 90 of their complaints related to Ryanair.
There were 62 complaints about flights cancelled by Ryanair out of a total of 93.
Aer Lingus attracted 15 complaints and 16 complaints related to 15 other airlines.
Ryanair accounted for 12 out of 20 complaints about long delays, compared to four for Aer Lingus.