Bringelly bus company operator Simon Lees and Narellan heavy vehicle inspector Stuart Lewry were both cleared of manslaughter by gross negligence charges in Wollongong District Court on Thursday following a four-week, judge-alone trial.

Family for both men broke down in tears when Judge Andrew Haesler delivered his verdict shortly before midday.

The court heard Simon's father, Graham Lees, was driving 29 passengers from Cabramatta to a retreat in Kangaroo Valley on the evening of May 14, 2010 when the brakes on his 53-seat Austral Skyliner failed, causing the vehicle to crash through a guard rail on a hairpin bend and career down a six metre embankment.

Mr Lees died instantly after he was thrown from the vehicle. Several other passengers were injured, one critically.

A seven-year investigation resulted in police laying manslaughter and grievous bodily harm charges against Simon Lees, 33, who was the company's operations manager at the time and who prosecutors had claimed was responsible for maintaining its fleet of vehicles.

Lewry, 43, was also charged with manslaughter over allegations he signed off on the bus' roadworthiness just days before the crash and without having physically inspected the vehicle.

However, Judge Haesler found the prosecution had failed to prove its case against both men.

Lawyers for Simon Lees told the court that the maintenance of the buses was the legal responsibility of the company's accredited operator and sole shareholder, Graham Lees.

"Graham Lees, we say, had the knowledge, responsibility and a legal duty in relation to the condition of the bus," defence lawyer Greg Heathcote said, adding decisions about major repairs on all the company's fleet of vehicles were made by the older Mr Lees.

More to come​