A fresh volcanic ash alert prompted Qantas to cancel one flight out of London and delay another for 11 hours, infuriating passengers after nearly a week of travel chaos.
As carriers worldwide resumed European services, the Australian airline cancelled a flight to Melbourne via Hong Kong and delayed QF8232 to Singapore and Sydney after being warned of a plume of ash on its flight path.
The Sydney flight finally took off at about midnight London time (2300 GMT), also carrying most of the Melbourne-bound passengers.
"We received information from the European airspace authorities that there's a plume on the air flight path," a spokeswoman told AFP on Thursday.
"That delay was made up of us assessing the situation and deciding if it was safe for us to fly.... Safety is our unwavering priority."
She said Qantas had a policy of not flying anywhere within 160 kilometres of clouds of volcanic ash, which can seize up jet engines by turning into molten glass.
Passengers were reportedly furious at the extra disruption.
"Every other airline that has flown out of Heathrow today has done so without any problem whatsoever," one traveller told Australia's AAP news agency.
"Qantas has no balls and they need to get final approval from CASA (Australia's Civil Aviation Safety Authority) to fly out of European air space," he added.
Corporate affairs spokesman David Epstein said Qantas had a policy of consulting CASA no matter where it was flying in the world.
"It's a safety-first policy... and we stand by it entirely," he said.
"Other countries have different regulatory systems and the fact is that we haven't lost a plane in the jet age and other countries have."
The airline said it was trying to put on extra flights to clear a backlog of 15,000 affected passengers, adding that most of those stranded in Singapore had already left.