Andrew Charles Richards, 40, was a senior executive for the federal organisation when he began what was later described as a sophisticated, persistent and pre-meditated fraud of the Australian Taxation Office.

Richards set up two fake businesses, which he called Infinite Aviation and the National Register of Encumbered Aircraft.

He then began submitting fraudulent business activity statements between 2007 and 2010, using them to claim GST refunds.

The ATO paid him $327,000, although he'd claimed much more.

He also attempted to claim a further $12,272.

When queried about some of the claims, he falsified tax invoices to third parties and bank statements to back them up.

Later, he tried to cover-up the crime by telling the ATO paper documentation relating to the businesses had been stolen from his car, and electronic files had been lost due to a hard drive malfunction.

He was eventually interviewed by ATO investigators, and made some admissions.

It would later emerge that even his job, a senior executive service level two, was obtained fraudulently.

Airservices Australia, which is responsible for air traffic control and air navigation services, does not hire people unless they are of good character.

He put down a fake date of birth and used white out and a photocopier to falsify his birth certificate, in an effort to avoid a police check.

That was designed to hide his criminal record relating to a past fraud.

Richards was sentenced to four years and two months imprisonment by Chief Justice Helen Murrell on Wednesday.

He will be released in two years and one month, but will remain on an order to be of good behaviour for a further two years and one month.

The whereabouts of the money was a "mystery", the court heard.

There was some suggestion it may have been used to support Richards' family.

There was also an indication he may have used it to fund the building of a biplane in his garage.

The court heard Richards suffered mental health problems, including anxiety, a panic disorder, and intermittent major depression.

He was raised in an unhappy environment, marred by his parents alcoholism and violence.

Richards was also diagnosed with testicular cancer in 2008, something his lawyer Michael Kukulies-Smith had "disinhibited" him during the offending.

Mr Kukulies-Smith said his client had believed he was going to die, particularly due to a family history of cancer.

He said there was nothing to suggest his client had used the money to live an extravagant lifestyle.

"I note there is no evidence of any significant personal benefit to my client," he said.

The court heard there was a considerable and unexplained delay in bringing Richards to court.

He was not charged until 2014, despite the evidence against him being ready years earlier.

That left him in limbo and meant he saw little point seeking employment, because he knew he would be sent to prison.

Richards hung his head as the sentence was handed down.

His likelihood of reoffending was linked with whether his mental health treatment continued.

Airservices Australia terminated his employment when it became aware of the charges.