Irish and Spanish aviation authorities launched an investigation into Ryanair on Wednesday after a Madrid to Paris flight had to be diverted to Tenerifelast weekend, citing technical issues.

CNBC reports on the troubles that Ryanair and its owner Michael O’Leary are facing. Last weekend’s diversion is but another mishap in the operations of Ryanair flights. In July, three flights were forced to emergency land in Valencia after low levels of fuel were reported.

Unions have accused Ryanair of "courting disaster" if it doesn't take action.

In a joint statement, Ireland’s Department of Transport, Tourism & Sport and the Spanish Ministry of Development said they would meet “to discuss oversight of Ryanair’s operation in Spain.”

Ryanair denies any accusations of “oversight in operation” and has accused Spanish authorities of falsifying information. The airline insists that it is safe and operates with sufficient amounts of fuel reserves.

The Irish pilots' union (IALPA) has claimed that Ryanair pressures flight crews to carry the minimum amount of fuel required under European regulations, but Ryanair has rejected these claims.

Ryanair said it has invited the Spanish Ministry to send a team of inspectors to Dublin to correct any "misplaced concerns" about Ryanair’s compliance with Europe’s operating and maintenance standards.

CNBC spoke with Victor Cook, a helicopter pilot about to obtain a commercial license from the Bristow Academy in Florida, who said, “From a business perspective I can understand that Ryanair is trying to lower their cost in all divisions across the company. By carrying less fuel, Ryanair is able to carry less weight, which reduces the amount of fuel they burn.”

Cook added, however, that fuel levels should not be dictated by the operator, but rather by the individual pilots on each plane as they are the ones who are ultimately responsible for the safety of the flight.

Ryanair is the largest passenger carrier operating in Spain, having carried more than 30 million passengers in the country last year.