Workers prepare to remove a crashed helicopter that collided with another helicopter in Gold Coast on 2 January. Photo: AFP/ handout / ABC
A report into the deadly mid-air collision of two helicopters above Australia's Gold Coast says the pilot of the helicopter coming into land did not hear a call over the radio by the pilot taking off.
But that does not mean that the taxi call was not made, according to a preliminary report released on Tuesday by the Australian Transport Safety Bureau (ATSB).
Two helicopters operated by Sea World Helicopters collided mid air on 2 January on the Gold Coast Broadwater.
Four people died, another six received serious injuries while three others sustained minor injuries in the crash.
One helicopter was destroyed and another was severely damaged but managed to land.
ATSB chief commissioner Angus Mitchell said: "It's important to stress that we are yet to make findings".
"The two helicopters collided at an altitude of about 130 feet, 23 seconds into the departing helicopter's flight," Mitchell said.
"The helicopters were operating in a non-controlled airspace where pilots use a Controlled Traffic Advisory Frequency to make radio calls to announce their positions or intentions, and where necessary to arrange separation from other aircraft," he said.
"The report details the calls made by the pilot of the returning helicopter and as they tracked south over the Broadwater, that they saw passengers boarding the second helicopter as it was preparing to depart.
"The pilot of the returning helicopter recalled that the assessment was that the departing helicopter would pass behind them and that they did not recall the pilot making a standard taxiing call, thereby announcing their intentions to depart.
"This does not necessarily mean that a taxiing call was not made."
The ATSB would undertake a detailed analysis of the radio calls that were made, Mitchell said.
"It will depend on what evidence we can get, not only recordings, equally from witnesses. There may be some things that we may not be able to completely determine," he said.
Sea World Helicopters pilot Ashley Jenkinson, New South Wales woman Vanessa Tadros and British couple Diane and Ronald Hughes died when the two helicopters conducting joy-flights collided near the Gold Coast theme park.
Three other passengers were critically injured including Geelong woman Winnie De Silva, her son Leon and Tadros's son Nicholas, who remains in hospital. Two New Zealand couples onboard one of the helicopters were also injured.
Arriving pilot did not see other helicopter depart
Two helicopters rest in water after colliding in mid-air in Gold Coast on 2 January. Photo: Handout / ABC / AFP
Mitchell said the report also detailed that the pilot of the arriving helicopter did not see the helicopter actually depart the helipad.
"While video footage taken by the passengers on both helicopters on mobile phones contained images of the other helicopter, this does not necessarily mean the other helicopter was visible to both pilots," he said.
"The investigation will look closely at issues both pilots potentially faced in seeing the other helicopter.
According to the report, two passengers on the inbound helicopter spotted the other taking off and at least one of them attempted to verbally alert the pilot.
When the verbal guidance did not work, a passenger physically tried to get the pilot's attention because they were concerned about a potential collision, the report said.
"The ATSB has already generated a 3D model view from the pilot seat from a similar EC130 helicopter, which we will use as part of a detailed visibility study to help the investigation determine the impediments both pilots may have faced in sighting the other helicopter."
Mitchell said the investigation would also consider the operator's procedures and practices for operating scenic flights in the Sea World area and the process in undertaking the recently acquired EC130 helicopters into operation.
"We will also review the regulatory surveillance of the operator and similar operators."
The investigation would also look at the use of the traffic collision avoidance system, noting that there was no requirement for the helicopters to be equipped with such a system, Mitchell said.
"I would like to finish by saying that I am acutely aware that those who lost a loved one in this accident and the survivors that are still recovering from significant mental and physical injuries and their families, want to understand not only how the tragedy unfolded, but equally, and most importantly, why it occurred," he said.
"And why didn't the safety equipment, processes and procedures, that are designed to prevent an accident like this, work on this occasion.
"But that's the ATSB's purpose and that is the purpose of our ongoing investigation, to uncover any safety issues that contributed or potentially contributed to this accident, and to encourage safety recommendations and safety actions so that similar accidents can be avoided in the future.
"In aviation, it is designed to the mature safety system where single points of failure should not exist.
"So we will be looking at everything that may have contributed, whether that be equipment, whether that be procedures, whether that be individual actions."
-ABC