The mid-air collision of two S-211 jets during aerial photography south of Melbourne highlights the importance of in-depth pre-flight planning of formation flying manoeuvres and strictly adhering to procedures and the agreed plan.
Two SIAI Marchetti S-211 ex-military jet trainer aircraft were conducting a formation flight over Port Phillip Bay on 19 November 2023, for aerial filming of both aircraft to promote a proposed television program.
The manoeuvre leading to the collision involved the formation lead aircraft, callsign 'Viper 1', rolling inverted before the second jet, 'Viper 2' passed directly beneath it. This manoeuvre had not been specifically briefed before the flight, and was conducted without the prior knowledge of the crew of Viper 1, the ATSB investigation of the accident found.
After the first attempt at the manoeuvre, the pilots of both aircraft discussed repeating the manoeuvre over the radio.
"This in-flight discussion did not allow the pilots to fully consider the risks associated with the manoeuvre before it was attempted for a second time," Chief Commissioner Angus Mitchell said.
During the second attempt, the right wing of Viper 2 struck the right wing of the inverted Viper 1. Viper 2 sustained substantial damage, resulting in the failure of its front wing spar and deformation of the outboard wing section, and an immediate loss of control. Soon after the aircraft impacted the water, fatally injuring both occupants (the pilot and a camera operator).
Viper 1 was not significantly damaged, having been struck on a section of wing where the structure is relatively stiffer and stronger, and was able to return safely to Essendon Airport.
"Pre-briefing of in-flight manoeuvres is critical to safe formation flying to mitigate the risks of increased pilot workload and distraction," Mr Mitchell said.
"Minimising the risk of these flights requires pilots to prioritise operational safety, in particular through in-depth briefings, pre-flight planning of manoeuvres, and strict adherence to procedures and the agreed plan.
"This ensures everyone has a similar understanding of the intended manoeuvres, and can fully consider the associated risks."
Pre-briefing of a manoeuvre can also be conducted in-flight, as done by the crew before the second attempt. However, when compared to a face-to-face pre-flight briefing, an in-flight briefing, using radio and while also flying the aircraft, limits a pilot's ability to articulate and understand intended manoeuvres and fully consider associated risks.
"In-flight briefings can also reduce the lead's ability to assess that there is mutual understanding before approving a manoeuvre," Mr Mitchell said.
The investigation also found the aircraft operator did not hold the required certificate to undertake the filming flight, which under CASA regulations is required to be conducted as an aerial work (task specialist) operation.
In addition, as ex-military aircraft operated in the Limited airworthiness category, the S-211s were not permitted to be used for that purpose.
Finally, the pilot of Viper 1 had medical restriction requirements which were not being fully followed during the flight (they were required to only operate aircraft with a side-by-side seating configuration and with a type-qualified safety pilot).
"While these factors did not directly contribute to the aircraft handling or decision-making that led to the collision, regulatory limitations exist to mitigate known risks associated with this type of operation," Mr Mitchell explained.
"Operating outside of these limitations removes in-built safety defences and organisational structures designed to identify and mitigate these risks."
