SINGAPORE (Reuters) – Qantas Airways Ltd, which hopes to buy planes this year for record-breaking 21-hour flights between Sydney and London has two hurdles left to overcome: getting pilots and Australia’s aviation regulator to agree to unprecedented duty times.

Airlines around the world are planning longer flights to compete with one-stop rivals and collect a fare premium of about 20 percent on non-stop routes, which are especially popular with corporate travelers.

Airbus SE and Boeing Co say their aircraft are ready, with only details like seat configuration left to hammer out, Qantas chief executive Alan Joyce said.

But there is a human cost to flying from Sydney to London or New York that must be resolved before tickets are sold, Joyce added.

“We don’t have the ability to do that length of duty today so you do need to negotiate that and get the regulator comfortable with it,” Joyce told Reuters in a phone interview. “If the business case works … (we can) put an order in by the end of this year and have aircraft arriving in 2022.”

Qantas pilots say the unprecedented length of the new flights means the airline needs do more research, consider more training, use more experienced pilots and change what they say is a flawed fatigue-reporting system.

    The maximum pilot duty time on the Sydney-London flights is expected to be around 23 hours, more than the current limit of 20 hours. “Duty” includes time on the ground before and after flights during which the flight crew is working.

Qantas already has 17-hour non-stop journeys between Perth and London with four pilots onboard.

Australia’s Civil Aviation Safety Authority (CASA) will evaluate the proposed longer duty time based partly on a study of pilot fatigue on the Perth-London route, agency spokesman Peter Gibson said.

It could approve longer hours, reject the proposal, approve a shorter duty time or require new measures like a more experienced crew or extended rest periods.