An air traffic controller did not issue a safety warning before two planes collided mid-air because he believed the pilots were already "sorting themselves out".
Peter Phillips, Ido Segev, Pasinee Meeseang and Christiaan Gobel were killed when the light aircraft collided at Mangalore in central Victoria on February 19, 2020.
Mr Phillips had been instructing Mr Segev on the VH-AEM aircraft, which was descending from about 6000 feet to carry out training closer to 4000 feet.
Ms Meeseang was being taught by Mr Gobel in the other plane, VH-JQF, which took off from Mangalore as the other aircraft was approaching the uncontrolled airspace.
John Tucker, the air traffic controller working that morning, told the Coroners Court on Monday there was sufficient separation between the two planes in the lead up to the collision.
He received four notifications through his traffic control system about potential conflict between the aircraft, but he did not issue a safety alert.
Two of those notifications happened 30 seconds before the fatal crash.
Mr Tucker told the inquest it was common for air traffic controllers to receive multiple conflict notifications that were either false or nuisance alerts.
He said the two planes appeared to be levelling before the crash so he assumed the pilots were communicating with each other on a different radio frequency.
"It looked like they were sorting themselves out," he told the inquest.
The planes crashed mid air at 11.24am and Mr Tucker issued a distress message after he was unable to reach the pilots.
A screen recording of the air traffic system was played to the inquest, showing what Mr Tucker saw and heard before the collision.
It showed from about a minute before the crash, the vector lines, or expected trajectory, of the two planes was likely to cross over.
The altitudes of the two aircraft were also dropping and rising respectively.
When questioned on whether those trajectories meant he should have made a safety alert warning, Mr Tucker queried whether the recording was correct.
"I'm really struggling to believe it's accurate," he told the inquest.
He said it was "hard to say" whether he would have acted differently if the recorded information was correct.
Mr Tucker said he believed he did everything required of him.
"I can only assume the aircraft were not communicating or keeping a look out," he said.
Outside court, Mr Segev's fiancee Brianna Sutcliffe said they were months from getting married when the tragedy happened.
The accident had ruined her life and the lives of many others, she said.
"The extent of pain and suffering this has caused ... is insurmountable and enduring," she told reporters.
"I will not rest until I receive transparency regarding the events surrounding the loss of my soulmate."
The inquest before State Coroner Judge John Cain is expected to run for four days.
