A Cathay Pacific flight and a Virgin Blue flight were two minutes away from a midair clash over the Australian Northern Territory.
A collision was avoided after Cathay pilots noticed the other aircraft and alerted air traffic controllers.
The Australian Transport Safety Bureau has launched a probe into the incident and a report is expected to be released in April.
Former Hong Kong director of civil aviation Peter Lok Kung-nam suspects negligence on the part of air traffic controllers and said it is something that should not have happened.
The Cathay Pacific flight CX135, an Airbus A330 carrying 309 passengers, was heading south to Melbourne from Hong Kong a week ago when the crew queried the flight path.
The Virgin Blue flight DJ1457, a Boeing 737 carrying 120 passengers, was flying north to Darwin from Melbourne.
The two aircraft were traveling at 37,000 feet and were 20 nautical miles (37 kilometers) away from each other.
Lok says the two aircraft would have had a closing speed of about 600 nautical miles per hour, meaning they would pass or collide in about two minutes if they continued on the same track.
Bureau investigators are treating the incident as
"serious." It is initially believed a Brisbane traffic controller was at fault.
"An appropriate avoidance action was taken by the Cathay Pacific crew. The matter is now under investigation by the Australian authorities and we have already filed a report to Hong Kong Civil Aviation Department," a Cathay spokeswoman said.
"It's not uncommon for aircraft to pass each other in flight and there are procedures in place around the world to ensure a safe separation," Virgin Blue spokesman Colin Lippiatt said.
Lippiatt added that what happened demonstrates the procedures that are in place work, and that it is not accurate to call the incident a near miss.
The two aircraft should have been the standard 29 nautical miles apart, according to Airservices Australia, which oversees air traffic control. They were both flying at 37,000 feet.
Both aircraft changed course and altitude to return to normal separation standards, Rob Walker, a spokesman for Airservices Australia, said.
"Its not unusual, but obviously we take them very seriously when they happen."
Walker added:
"It would be premature to go into the reasons why it happened. A multitude of things can come into play. The investigation will go into the exact details."
The probe will look into the standards used to keep aircraft safe distances from each other, bureau spokesman Neville McMartin said.
An initial investigation report said
"there was a breakdown of separation standards," with neither aircraft being damaged during the incident.
Lok said there are collision avoidance systems on aircraft.
"Two minutes is a long time [up in the air], but something that shouldn't have happened did happen."
Source: Aviation Week