SYDNEY (BLOOMBERG) - Proposed flights half way around the globe are set to be even less comfortable than expected. That is, if the marathon 20-hour non-stop services from Sydney to London get off the ground at all.

Qantas Airways ditched the notion of rolling out bunks, beds, a gym or even a creche for passengers enduring the world's longest commercial flight. Instead, they'll be given a space to have a stretch and a drink of water, Qantas chief executive officer Alan Joyce said Monday (June 3) in Seoul.

The more spartan comfort levels underscore Qantas's challenge as it tries to break through what it calls aviation's last frontier. There are other barriers, too: While Mr Joyce said the planes proposed by Boeing Co and Airbus SE for the ultra long-haul flights can make the distance, neither can carry the weight that Qantas initially targeted.

Speaking to reporters in Seoul at the annual gathering of airline bosses, Mr Joyce said he still needs Qantas pilots to agree to the longer working hours the ultra-long flights will entail.

"There are a significant number of hurdles to overcome but we think we can make this work," he said. "There's still not full payload on each aircraft, but there's enough we think to make it commercially viable if the other parts of the business case get there."

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Qantas expects to receive final aircraft proposals from Boeing and Airbus by August. That will include the price of the plane, as well as guarantees on fuel efficiency, maintenance costs and reliability.

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Mr Joyce said he will order the jets by year-end if he decides to push ahead with the flights, which are known at Qantas as Project Sunrise.

Qantas has said it is sizing up the long-range Airbus A350 against Boeing's 777X. Boeing or Airbus would deliver the aircraft in 2022 and the first flights would be in 2023, he said.

Still, there is little margin for error. For example, the Sydney-London service won't be able to carry extra freight, Mr Joyce said. Direct flights to New York from Sydney are more achievable, he said.

Qantas is trying to roll out a network of super-long direct services connecting Australia's eastern seaboard with South America, South Africa and North America as rising oil prices squeeze profit margins.

Even after promoting Project Sunrise for years, Mr Joyce said he would be ruthless. "We will kill the project" if the economics don't stack up, he said.

Mr Joyce said the planes will have sections for first class, business, premium economy and economy passengers.