Four hundred workers will lose their jobs as Qantas Airways overhauls its engineering operations.
Qantas says the decision to cut 150 of its own workers and 250 contractor positions is due to overstaffing at its line maintenance facility in Sydney, and as work on cabin interiors of Boeing 747-400 aircraft was completed at Avalon.
Jobs were also being shed at Qantas Defence Services - which maintains the Australian Defence Force's C130 Hercules aircraft - and as the carrier consolidated its engineering training facilities from Melbourne to Sydney.
Qantas domestic chief executive Lyell Strambi said newer aircraft arriving into the fleet required less maintenance than the older aircraft they were replacing.
"I believe we have some of the most highly skilled and capable engineers in the world," Mr Strambi said in a statement on Thursday.
"Unfortunately we just have too many for the work we have right now and the work we expect to have in future."
Australian Licenced Aircraft Engineers Association federal secretary Steve Purvinas said the Qantas job cuts threatened safety.
"In our view, the current levels of understaffing are becoming dangerous and Qantas management are disregarding basic laws of aviation safety," Mr Purvinas said in a statement.
"This needs to stop or Qantas risks becoming an unsafe operator."
Line maintenance is carried out on aircraft daily, usually in between flights or overnight, and includes minor repairs or modifications and visual inspections.
Mr Strambi said the restructure would assist in making Qantas maintenance facilities in Australia more competitive.
"Qantas has an outstanding track record in aircraft maintenance, and our commitment to setting a global standard for safety and quality in airline maintenance will never change," Mr Strambi said.
Affected staff would be offered assistance to relocate to Brisbane, or redeployment to other roles at the company, he said.
Australian Workers' Union Victorian secretary Cesar Melhem urged Qantas to make every effort to redeploy those losing their jobs at Avalon.
"These are highly-skilled aviation mechanical engineers who have worked to help build the Qantas reputation for safety," Mr Melhem said in a statement.
"It is unthinkable that they are cast aside in this way."
At the same time as the 400 jobs were being cut, Qantas said it was adding up to 120 positions at its Brisbane maintenance facility as work was transferred from the airline's Tullamarine site in Melbourne, which closed in August.
The airline said it had already added 100 positions in Brisbane since May.
Qantas has said previously it planned to eventually consolidate all its heavy maintenance work for Boeing 737, 767 and Airbus A330 aircraft on one site.
Brisbane was regarded the most likely option given recently announced plans to spend $30 million on upgrading the heavy maintenance facility, leaving Avalon to be eventually shut down.
Thursday's announcement was the latest round in a series of job cuts at Qantas.
In May, Qantas said it was closing its heavy maintenance facility at Tullamarine in Victoria, with the loss of 422 jobs.
Qantas and its partner Lufthansa also confirmed in July its joint-venture engine workshop at Tullamarine would close, impacting 164 jobs.
Qantas closed down two cents at $1.28.