Qantas will stop using Darwin as a hub for one of its London services after the war in the Ukraine restricted the number of passengers the airline could transport on the flights.
The national carrier says the QF9/10 service will fly via Perth between Melbourne and the UK so more seats can be made available to travellers.
"Our flights from Darwin to London are currently operating with reduced passenger numbers," a spokeswoman said in a statement on Wednesday.
"This is due to the effective closure of Russian airspace, which means we have to carry extra fuel to fly an alternative longer route."
Qantas said the Perth to London route was shorter, which meant less weighty fuel was needed and more passengers could be carried.
The airline temporarily rerouted its London flights from Perth to Darwin in November after the West Australian government announced it was unlikely to reopen its borders to international travellers amid the COVID-19 pandemic.
"The NT government and Darwin Airport went above and beyond so that we could operate these services when WA kept its borders closed, and we're extremely grateful for their partnership," Qantas International chief executive Andrew David said.
The QF1/2 service in and out of Sydney will continue to operate direct between London and Darwin as scheduled until June 18 when it will return to Singapore.
The first Perth to London flight will depart on May 23. They were previously scheduled to return to Perth from June 19.
It comes amid complaints that damage to the Darwin airport runway reportedly caused Qantas to leave some passengers' luggage in the Territory capital in a bid to reduce weight on a recent London flight.