A cockpit display or electronic flight bag app showing traffic information from ADS-B IN data would have alerted the pilots of two training aircraft involved in a fatal mid-air collision near Mangalore, Victoria to the position of the other aircraft much earlier compared to visual acquisition, an Australian Transport Safety Bureau study concludes.
In March, the ATSB released its final report from its investigation into the accident which found that, following receipt of verbal traffic information provided to both aircraft by air traffic control, the pilots of both aircraft did not successfully manoeuvre or establish direct radio communications to maintain separation, probably due to not recognising the risk of collision.
The accident was the first mid-air collision between two civil registered aircraft operating under the instrument flight rules (IFR) in Australia. As the collision occurred outside of controlled airspace, air traffic control (ATC) was required to provide traffic information on other IFR aircraft but was not responsible for ensuring separation. This meant that the pilots were self-separating using radio communications and, where possible, the ’see and avoid’ principle.
‘See and avoid’ has known limitations, and central to the investigation was determining the likelihood that the pilots of each aircraft could detect the other visually in sufficient time to take avoiding action.
“To support the investigation, the ATSB initiated an aircraft performance and cockpit visibility study to determine when each aircraft may have been visible to the pilots of the other aircraft,” said ATSB Chief Commissioner Angus Mitchell.
“In addition, the study was undertaken to determine what effect an ADS-B IN system would have had on the pilots’ ability to detect traffic as they converged.”
Aircraft fitted with ADS-B OUT transmit positional and speed information derived from GPS to receivers including those used for air traffic control. Aircraft fitted with ADS-B IN equipment can receive this information on nearby aircraft, aiding pilot situational awareness.
Mr Mitchell said the investigation found that the pilots had insufficient time to visually acquire the opposing aircraft as cloud likely obscured the aircraft up until the collision, and added the study found that even in clearer conditions the aircraft were unlikely to have had sufficient time to visually acquire one another in time to avoid a collision.
“Analysis indicated that even in clearer conditions than experienced on the day of the accident, closing speeds and shielding by the aircraft structures would have limited the pilots’ opportunities to acquire the other aircraft, with two of the four pilots involved likely having the opposing aircraft shielded from their view at key moments prior to the collision,” he said.
As part of the study the ATSB developed scale three-dimensional models of the internal and external structures of representative aircraft using laser scanning technology, and determined the pilots’ approximate eye position within each model.
Investigators then developed animations using ADS-B position and aircraft performance data showing the cockpit view for both pilots in each aircraft overlaid with simulated cockpit traffic displays and alerts. This was supplemented by recorded air traffic control data.
These animations help illustrate the limitations of visual acquisition. Moreover, they demonstrate the significant additional alerting time that would be provided by an ADS-B IN display with an aural alert.
“The study has clearly shown that had the aircraft been equipped with ADS-B IN, the pilots would have been assisted in locating the other aircraft and alerted to its position much earlier than by visual acquisition,” Mr Mitchell said.
“The ATSB continues to strongly encourage the fitment and use of ADS-B transmitting, receiving and display devices in all general and recreational aviation aircraft, as these devices can significantly assist pilots with the identification and avoidance of conflicting traffic, and are available at relatively low-cost.”
While both aircraft involved in the mid-air collision were equipped with ADS-B OUT, neither aircraft were equipped with ADS-B IN systems, and nor were they required to be.
“Both a cockpit display of traffic information with an ADS-B traffic alerting system or an electronic conspicuity device connected to an electronic flight bag application could have provided this advance warning of a potential collision to the pilots of both aircraft,” Mr Mitchell said.
“While effective radio communication remains the primary means of self-separation in non-controlled airspace, the targeted and accurate information provided by ADS-B IN can provide pilots with significant assistance.”
Read the aircraft performance and cockpit visibility study: AS-2022-001 – Aircraft performance and cockpit visibility study supporting investigation into mid air collision of VH-AEM and VH-JQF near Mangalore Airport Vic. on 19 February 2020
More information about ADS-B and the benefits of using the technology: Automatic Dependent Surveillance Broadcast – Airservices