The amount of compensation and refunds secured by the Commission for Aviation Regulation for air passengers on foot of complaints soared by more than 60% last year.
The Regulator's annual report showed that it tackled a backlog of complaints which resulted in €648,475 in compensation and €92,865 in refunds and reimbursements being paid out to air customers - an annual increase of 61.6%.
Also last year, the CAR received 1,940 passenger complaints against airlines - 18% lower than in 2018.
According to the report: "In 2019 the Commission received written complaints and queries from 4,682 individuals, an increase of a little over 4% on the number received in 2018.
"We also received 1,857 telephone calls from 1,609 individuals, a 32% decrease on last year.
"This was in part due to an improvement in investigation turnaround times and a reduction in the number of update requests."
Some 62% of complaints were due to long delays while a third were due to flight cancellations.
Overall, complaints were investigated against 56 different airlines during the year.
Aer Lingus were the subject of 31% of the complaints (485), Ryanair accounted for 28% (433) and Norwegian 4% (62). Vueling, KLM, Lufthansa and TUI each accounted for a further 3% of complaints.
Of the 1,212 concluded investigations 650 or 44% were upheld with the remaining 56% not sustained.
In the report foreword, Commissioner Cathy Mannion said new members had been added to the team charged with addressing complaints in the second quarter of last year, with a view to tackling the backlog.
Among the Regulator's responsibilities is the investigating of complaints about flight cancellations, delays of at least two hours and instances of denied boarding or downgrading for all flights due to depart from Irish airports and for flights arriving into Irish airports from non-EU countries, as well as complaints relating to the assistance received by passengers with reduced mobility when making a reservation, travelling through an airport within Ireland or boarding a flight leaving from an Irish airport.
In 10 of the 12 complaints involving Persons with Reduced Mobility infringement of regulations was noted by the Regulator.
Last October the Regulator published its Final Determination on the maximum level of airport charges at Dublin Airport starting from January 2020, but it admitted in the report that "the wide-ranging impact of Covid-19 means that many of the assumptions and expectations which underpin the 2019 Determination on airport charges are no longer reflective of reality".
The report also outlined the pressure on time slots for take-off and landing at Dublin Airport, saying "over the last number of years, with the substantial growth in demand, Dublin Airport has become increasingly slot constrained".
As for slot misuse, it said one new sanction was issued in 2019, to Ryanair, in relation to an operation without a slot.
The total amount sanctioned was €3,000 while an €8,200 sanction issued to Aer Lingus in 2018, in relation to off slot operations in 2018, was also finalised.
In her report foreword, Ms Mannion also referred to the developing situation regarding Covid-19.
"The Covid-19 global pandemic is having a devastating impact on the global aviation and travel industries and on economic activity generally," she said.
"In 2020, we will refocus our priorities and work programmes to ensure that we provide regulatory responses that both support the recovery of the industries that we regulate and ensure that the interests of passengers remain to the fore.
"Our revised work plan will include the possibility of at least one interim review of the price determination for Dublin Airport and a new performance plan for air navigation services under the single European Sky regulations."