A review of spending on the Government's Regional Airports Programme (RAP) has found it is difficult to offer strong conclusions about whether it is meeting its connectivity objectives, because of a lack of well defined objectives or targets.
The analysis, by officials in the Department of Transport, Tourism and Sport, says consideration should be given to defining connectivity indicators in any such future programmes.
These would include measures such as the number of services, number of routes operated and number of passengers.
The RAP provides capital grants and operating subvention to Donegal Airport, Farranfore (Kerry) Airport, Ireland West Airport Knock (IWAK) and Waterford Airport.
It also provides funding for two Public Service Obligation (PSO) domestic air services between Donegal-Dublin and Kerry-Dublin.
Its purpose is to ensure that financially unviable air connectivity can be provided to Ireland's more isolated regions for economic and social benefit.
Overall the report, which is part of the Government's Spending Review 2019, says the objectives of the programme are found to be largely consistent with Government priorities in respect of regional development.
It also states that the provision of regional air services would be extremely challenging without Government intervention.
It says passenger numbers have been rising steadily at all the airports, except Waterford where there are no commercial scheduled services.
However, increased safety and security requirements as well as improved Government finances, the subsidies for operating costs have also increased in recent years, it finds.
In 2012, for example, the total cost of airport expenditure under RAP was €14.31m, but by 2018 that had reached €15.46m.
The Donegal and Kerry PSO services have seen significant passenger growth in recent years, it also says, as the economy has recovered.
The result of this, the study finds, is that the PSO subsidy per passenger and per seat has decreased substantially since 2012.
If the PSO services are renewed after the current contract ends later this year, the revenue impact of the increased passenger numbers may provide scope to reduce the overall level of subvention provided, it suggests.
Donegal Airport is found by the analysis to serve the most remote region of Ireland and so according to the authors, "there would appear to be a strong justification for a PSO service to Donegal Airport".
Kerry Airport is found to have the largest local catchment of all the regional airports, although it overlaps with the catchments for both Cork and Shannon airports.
But the report says that while Kerry Airport is more than three hours by road from Dublin, its proximity to Cork "should be considered when considering the future of its PSO service particularly when road improvements have been completed".
The study also concludes that there is little justification for PSO routes to Waterford Airport because of its proximity to Dublin and to Ireland West Airport Knock because it is around three hours from Dublin and close to Galway by road.