Qantas used Changi prisoners

Qantas has used prisoners from Singapore's Changi Prison to clean aircraft, an engineers' union says.

However the airline denies prisoners at the jail have had access to Qantas aircraft undergoing maintenance.

The Australian Licensed Aircraft Engineers Association (ALAEA) federal secretary Steve Purvinas used the parliamentary privilege of a Senate inquiry to say prisoners from the Singapore jail were brought in to clean planes before scheduled deep maintenance.

"The prisoners are released under supervision and taken to the Qantas aircraft," Mr Purvinas said.

"The prisoners are used to wash down the wheel-well bays before inspections, they're used to go upstairs into the flight deck of the aircraft and to clean the area out so it's ready for inspection by the local engineers."

Changi Prison houses Singapore's most serious criminals, including those sentenced to death.

Melbourne drug trafficker Nguyen Tuong Van was hanged at Changi in December 2005 after being convicted of trying to smuggle almost 400 grams of heroin through Singapore to Australia.

Qantas was unable to categorically deny the use of prisoners in all of its operations, despite requests.

However, the national carrier issued a statement saying it did not allow prisoners access to aircraft undergoing maintenance.

"Qantas categorically denies the union's outrageous claim regarding prisoners," executive general manager of Qantas engineering David Cox said in a statement.

"No prisoners have access to any Qantas aircraft undergoing maintenance - in Singapore or anywhere else."

It is understood the aircraft cleaning and maintenance is contracted out to a subsidiary of Singapore Airlines, Sasco.

Sasco did not return calls asking for comment on the allegations.

The company operates at both Changi and Paya Lebar airports and is endorsed by Australia's air safety regulator the Civil Aviation Safety Authority.

Mr Cox said he had spoken with a contractor, without confirming it was Sasco.

"I took to the effort to go and call them, this Singapore engineering company, I got a very categoric assurance that this is not true," Mr Cox told ABC Radio.

An official from the union, who spoke on condition of anonymity, said Qantas had been made aware of the allegations years ago.

"They were very defensive," the official said.

Mr Cox claimed the union's allegations were part of on-going industrial protests in the wake of the proposed sale of Qantas to private equity consortium Airline Partners Australia.

"This is part of an industrially motivated campaign by the ALAEA aimed at protecting uncompetitive work practices in Australia," Mr Cox said