THEY were recruited to address Australia's critical shortage of air traffic controllers, but the latest crop of trainees at the Airservices Australia learning academy are effectively twiddling their thumbs because there are not enough instructors to teach them, academy sources and the air traffic controllers union say.

Airservices Australia has repeatedly claimed it is addressing the shortage - which is resulting in large areas of air space going unmonitored each day - by dramatically increasing the number of new recruits each year.

But a staff member from the Melbourne academy says the latest intake of around 15 trainees have been given jobs running an air-traffic simulator program and told their training will not begin for three months because there are not enough instructors.

"The simulator program requires people to act as pilots while others learn how to be controllers; they're called simulator service operators and Airservices already employs people to do that," the staff member said.

"But because there are no instructors, that's what the latest group are being told to do all day. There is virtually no benefit other than to learn a bit about what it's like to be a pilot."

Any delay in the training of the recruits would be significant given the safety problems created by the air traffic controllers shortage.

Large sections of air space go unmonitored almost every day and there have been a number of highly publicised mid-air near-misses, which some in the industry have blamed on the shortage.

The Civil Aviation Safety Authority recently stepped in to limit the number of passenger jets allowed to fly through the uncontrolled zones.

Airservices says it has increased the intake of new recruits from 48 last year to 80 this year and 100 in 2009.

It strongly denied there was any shortage of instructors and said trainees spent more than 70 per cent of the course in the simulator where they developed practical skills. It did not specify what role they took in the program.