Donegal Cancer Flights and Services says almost 1,000 medically related flights were recorded in a single year.
Last year, the group logged 958 individual flight legs on the Donegal to Dublin Public Service Obligation route.
The flights were used by cancer patients travelling for treatment, as well as the carers who accompanied them.
Almost €40,000 was spent on those journeys, funded entirely through community fundraising.
The organisation says a Public Service Obligation route must provide reliable, same day access for patients.
It warns that without a workable midday return service, a single cancellation can disrupt critical treatment plans.
