Amid global focus on the aviation industry as the world waits for fresh developments about the missing Malaysian Airlines Flight 370, the aircraft engineers' union at Qantas warned of a possible aviation disaster waiting plans of the Flying Roo.

The union claimed there are so many errors on Qantas jets that are sent to Asia for heavy maintenance over the years, risking passenger lives. It cited maintenance done on a Qantas Boeing 747 aircraft in which three of its four engines were allegedly improperly attached.

The revelation is part of the union's attempt to prevent the federal government from amending the Qantas Sale Act. Australian Licensed Aircraft Engineers Association Federal Secretary Steve Purvinas released a dossier that contains the alleged multiple errors on Qantas jets after the airline moved heavy maintenance to Singapore, Hong Kong and Kuala Lumpur.

The submission that Mr Purvinas released claimed there are about 600 defects on the first Qantas 737 plane when the jet was sent to Singapore for heavy maintenance in late 2009. It includes corrosion on the wings, cracked floor beam, damaged wiring and loose of defective wiring clamps.

The wrongly attached engines of a Qantas 747 jumbo aircraft was done in Hong Kong, while heavy maintenance in Kuala Lumpur in 2008 resulted in 95 errors on a Qantas 737 such as extensive corrosion on fuselage doors and wings and rusty flight control cables.

However, in defense of the overseas heavy maintenance work, Qantas Chief Executive Alan Joyce said all Qantas jets were certified by local regulators and Australia's Civil Aviation Safety Authority. He said mistakes were fixed when discovered and levels of error did not exceed those when maintenance work was done in Australia.

Despite the opposition of the unions to the job cuts, which are part of the $2-billion cost reduction strategy of the flag carrier, Mr Joyce said he is determined to push through with it, insisting that axing jobs could not be avoided.

"We have to male, I will say again, some tough decisions. It is not easy having to make 5,000 people redundant," ABC quoted the Qantas chief executive.

He pointed out that other airlines are also cutting costs to survive, citing the case of Japan Airlines which had announced a plan to axe 21,000 positions or 30 per cent of its workforce.

He also cited similar moves by Lufthansa and American Airlines.