There was a 56% increase in complaints against airlines that use Irish airports in the last year.
Figures from the Commission for Aviation Regulation (CAR) show it handled 4,420 passenger queries.
Of these, 2,319 were classed as valid complaints.
Some 70 of these related to the rights of disabled persons and persons with reduced mobility when travelling by air.
However, just 19 of these complaints were within the CAR's remit.
The remaining 2,319 complaints related to possible infringements of passenger rights.
Of the total complaints, 101 related to flights departing from airports in other member states - or flights arriving into such airports from non-EU countries.
Some 2,218 complaints were subject to a full investigation by the CAR - an increase of 126% on 2017.
It also investigated eight complaints about possible unlicensed trading during the year.
The CAR says as a result of the increased volume, it has "further strengthened" its Air Passenger Rights team for this year.
Aviation Commissioner Cathy Mannion says: "The mission of the Commission for Aviation Regulation is to protect the interests of air passengers.
"This mission crosses all our functions, from ensuring passengers at Dublin Airport are offered efficient and high-quality airport services to ensuring that customers of airlines, travel agents and tour operators have an appropriate level of protection."
"We also ensured passenger rights were respected and the handling of valid complaints meant that we obtained €458,817 for passengers affected by flight disruption."
"The volume we receive has grown significantly in the last two years and has impacted on how quickly we can deal with each complaint."
The CAR says it will monitor the impact that Brexit may have on the volume of complaints and queries received.
But it notes that if the UK leaves the EU, "all complaints relating to flights entering Ireland from the UK on EU registered carriers may need to be investigated by this office."
The CAR investigates 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.
It also investigates complaints for flights arriving into Irish airports from non-EU countries, if they are operated by EU-licensed carriers.
Its remit also covers complaints relating to the assistance received by passengers with reduced mobility, travelling through an airport within Ireland, or boarding a flight leaving from an Irish airport.
Read the report in full here