Airbus has tentatively identified an A330-200 derivative as the most promising long-term candidate to replace its five A300-600ST Beluga oversize transports.

The airframer has already embarked on a programme to restructure its A300-600ST operations to cope with the demands of ramped-up production over the next four or five years.

This programme, designated Fly 10,000, is intended to increase the flight work performed by the transport fleet to 10,000h per year in 2017, from the current level of about 6,000h.

Airbus says it is changing "ways of working, opening hours and organisation" to meet this demand, which would double the number of weekly flights to around 120.

The greater Beluga workload will primarily arise from a surge in A350 output. But Airbus will also require capacity for the A400M, which will partly offset a decline in A330 production, while A320 and A320neo rates are set to remain high.

Airbus recently indicated to Flightglobal that the A300-600ST fleet would probably remain in service for another 10 years or so.

But while the fleet could remain in service until around 2025, the cost of operating the type will increase as the aircraft age. The airframer has initiated a study to replace the A300-600ST fleet in the long term.

"No decision for immediate launch has been taken," it stresses. But to address any capacity limitations beyond the Fly 10,000 scheme as well as the ageing of the current Beluga fleet, Airbus is likely to aim for 2018-20 as a window to have a new aircraft available.

Several airframes are being considered as a platform for a Beluga successor, notably the A330-200 and -300, as well as the A340-500 and even the A300-600.

The current Beluga fleet carries A350-900 fuselage sections, and is capable of handling the A350-1000, although the final cross-section for any new transport has yet to be fully determined. The A300-600ST has a hold diameter of about 7.1m.

Airbus wants an aircraft which not only meets high payload capabilities - including capacity to carry two fully-fitted A350 wings - but can operate within airfield landing limitations at its UK wing facility at Broughton, to which it will deliver A350 wing covers.

Broughton's declared available landing distance for the shorter runway 04 approach is 1,663m (5,460ft).

Airbus considers this restriction to be too tight for a modified A330-300 or A340-500, while the payload requirement is too high for an A300-600. It believes an A330-200 variant - tentatively designated the A330-200XL - could potentially cope with the landing criteria at projected weights of around 135t, and is the most promising option.