Qantas has refused to rule out sending more engineering work offshore as unions stepped up their fight to prevent checks on one of the carrier's 747s being carried out in Singapore.

Qantas head of engineering David Cox said the airline made no secret of the fact it was "actively in the market" to make sure plans were in place in case work could not be done in Australia.

"In an average year we would have anywhere between 10 and 20 of our heavy maintenance checks done offshore," he said.

"So far in 2005-06 we've done 10 offshore, so we're still at the very low end of the average of recent years."

Qantas has been at loggerheads with its engineering unions since it announced last month that it would close its heavy maintenance operations in Sydney by the end of next month.

It is transferring the work to Brisbane and Avalon, Victoria, with a net loss across the company of 340 jobs, more than 200 of them licensed engineers.

Mr Cox said the airline was now doing more of its work in Australia than at any time in the past four or five years.

But he said he was not ruling out sending more aircraft overseas. "Quite the opposite," he said. "I'm saying that if we need to do it, looking out ahead, we will be prepared and we're making no secret of that.

"The other thing I will say is that as soon as we know, we will consult with people."

About 35 engineers protested outside the Australian Industrial Relations Commission yesterday as their union attempted to stop the 747 work going to Singapore.

Australian Licensed Aircraft Engineer Association industrial manager Chris Ryan said the union believed work on two more Qantas 747s was going offshore.

Mr Ryan said the union wanted to move work from Avalon to Sydney so the 747 work could be done in Victoria, and was developing a business plan to allow Qantas to do this.

This would mean keeping some Sydney heavy maintenance operations open beyond the May deadline.

"What we're in the commission trying to do is manoeuvre the company so they have no choice but to ... consider a business plan we might put (to them)," he said.

Mr Cox said he had not seen a business plan from the unions but the forces driving the Sydney closure were so great that the airline would not reverse the decision.