Paschal Donohoe (Dublin Central, Fine Gael) | Oireachtas source

There would be two reasons. My understanding is that in 2014 there were 19 refusals. Permission was refused on the basis of the advice of the Department of Foreign Affairs and Trade.

If that refusal happened they were then required to reroute, so they were not allowed through Irish air space.

Regarding the rationale as to why that would be the case, the stated policy of the Department of Foreign Affairs and Trade is that it will not allow material or munitions to be carried through our air space that would be indiscriminate in nature and that would have a general effect were they to be used. On that basis, that is one of the main reasons for which such a refusal would be recommended.