Qantas and Jetstar have won a Federal Court case launched by a union after ordering aircraft engineers to stop work without pay amid the COVID-19 crisis.
From late March and early April, the airlines stood down hundreds of maintenance staff along with about 20,000 other employees including pilots and cabin crew.
After the COVID-19 fallout both companies progressively experienced a reduction in passengers, with Qantas eventually suspending all international flights citing government restrictions on travel.
An application to the Fair Work Commission was made by the Australian Licensed Aircraft Engineers Association in March.
The union argued it was a business decision in response to "actual and projected downturn in trade", an event within the airlines' control.
"It is a stoppage arising from a voluntary change in business operations, not a matter entirely out of the airlines' hands," the court was told.
But the Qantas Group, which includes Jetstar, said it had already explored and implemented every other cost-saving measure, such as ceasing payments for rent, and these were not sufficient.
On Tuesday Justice Geoffrey Flick ruled the "stoppage of work for both Qantas and Jetstar ... was one for which Qantas could not reasonably be held responsible and one which Jetstar could not reasonably prevent".
"Given the substantial downturn in passenger flights, there was no other option 'reasonably' open for Qantas or Jetstar to pursue," he said.
He ruled the licensed engineers could not be "usefully employed" during the stand-down period, and the airlines were pursuing a course "of ensuring their very economic survival".
The total wage bill for Qantas aircraft maintenance workers at the time was about $3.8 million a week, and for Jetstar, about $500,000 a week.
Due to the pandemic Qantas and Jetstar will reportedly continue to run at a loss for the 2020/21 financial year.