German air navigation service provider DFS has billed Ryanair nearly €450,000 ($610,000) for allegedly understating its aircraft's maximum take-off weight in ATC fee calculations, while EuroControl is also reviewing its route charges with the Irish budget carrier.
DFS stresses that Ryanair's pilots used correct takeoff weight data for their flight preparations and performance calculations. But the ANSP claims that the airline submitted 67t as MTOW for the calculation of terminal fees, whereas 75t would have been the correct value for the airline's Boeing 737-800 fleet.
Terminal and route fees are based on the aircraft's MTOW rather than actual weight on the individual flights.
Certain aircraft, such as the 737, are sold with multiple MTOW values. But Eurocontrol says that the highest value should be employed for the calculation of route charges.
The authority says it "largely relied" upon the airlines' own weight declarations in the past. But it adds: "We became aware some time ago that there is an issue with the declarations of Ryanair and, for some months now, we have been actively attempting to address the issue with Ryanair, as well as reviewing the operation of the system more generally."
For the calculation of route charges in 2013, the authority says it will apply "what we consider to be the correct values of MTOW" which in Ryanair's case is 74,990kg.
Ryanair responds that it operates its aircraft in accordance with Boeing's "flex-weight programme", which has been approved by the Irish Aviation Authority and is employed by a number of carriers. Both Ryanair and the regulator have declined to specify the circumstances which allow varying the aircraft's MTOW.
DFS says that it is possible to reduce the value if the aircraft is deployed on short routes which require a smaller fuel load. But the ANSP adds that this does not apply to the Ryanair flights from German airports since 2009, which it has been investigating.
DFS noticed the discrepancies in 2012, when it compared Ryanair's data with that of other operators. It has now sent the airline a bill of around €447,000.
The ANSP says that it has only been able to check records for flights since mid-2009 and that potential previous discrepancies would be barred from any claims.