The Irish Aviation Authority said today that Ryanair should review its fuel policy after three planes made emergency landings in Spain in July.
However, it did say that the planes were carrying more than the required amount of fuel.
The recommendation came after Irish and Spanish aviation officials met in Dublin this week following comments by Spanish authorities about incidents in their airspace involving Europe's largest budget airline.
Spain has called for tighter safety regimes at low-cost airlines.
Ryanair has accused the Spanish aviation authorities of falsifying information on incidents involving its planes, an accusation Spanish officials have rejected.
In a preliminary report made public by Ryanair, the IAA found that the three planes that departed for Madrid were carrying fuel in excess of requirements.
Having to divert to Valencia with fuel close to the minimum diversion level likely presented challenges to the crew, it added.
It recommended that Ryanair review its fuel policy and consider issuing guidance to crew with respect to fuel when flying into busy airports, particularly in poor weather conditions when diversions were likely.
The IAA also advised the Spanish aviation authority to review delays into Madrid and whether it should recommend that additional fuel be carried during normal operations.
Ryanair said the report disproved claims in Spanish media that its aircraft carried less than minimum fuel and were in breach of EU regulations.