Airbus has yet to disclose detailed final specifications of the adapted A350-1000 which will be developed for Australian carrier Qantas’s Project Sunrise ultra-long-haul flights.

The provisional selection of the twinjet by Qantas is still to evolve into a firm order, owing to continuing negotiations over various aspects of the envisioned New York-Sydney and London-Sydney flights.

But the airframer stresses that the proposed aircraft, while “based on” the -1000, is “not a ULR”, suggesting that it is not intending to produce an equivalent modified version of the -1000 in the same way that it developed the A350-900ULR for ultra-long-haul services.

Airbus has not confirmed the range or final maximum take-off weight of the Sunrise aircraft, but has been putting forward a 319t version of the Rolls-Royce Trent XWB-powered jet.

No further details are being disclosed about the extra fuel capacity, although Qantas has stated that the jet will have an additional tank. The A350-1000 currently has a declared fuel capacity of 156,000 litres.

But Airbus states that the aircraft will be capable of operating both directions on the London-Sydney route.

Further specifications are likely to be released only once Qantas has reached a firm decision on launching the Sunrise flights.

FlightGlobal understands that, although technical details of the aircraft are still being finalised, the primary issue to be resolved relates to crew working conditions.

“Airbus has given us an extra month to lock in an aircraft order without impacting our planned start date, which means we can spend more time on hopefully reaching a deal with our pilots,” says Qantas chief Alan Joyce.

“We’re offering promotions and an increase in pay but we’re asking for some flexibility in return, which will help lower our operating costs.”

Joyce says the choice between the A350-1000 and the rival Boeing 777X was “tough”, particularly because both airframers had been working to improve on two aircraft which were already “very capable”.

Qantas is looking at ordering up to 12 A350-1000s to serve Sunrise routes, although the carrier has previously indicated that such a commitment could be staggered.