A fateful request to redo an unplanned trick sparked a deadly mid-air plane crash over Victoria's Port Phillip Bay, the national transport safety investigator has found.
Pilot Stephen Gale, 56, and cameraman James Rose, 30, were killed when one of two Viper S-211 Marchetti planes went down on November 19 during a formation flight.
They were filming to promote a mooted TV program, Any Fool Can Fly, when the former fighter jets collided about 12km west of Mount Martha.
Their bodies were later found off Mornington in the wreckage of their plane, known as Viper 2, submerged in 22 metres of water.
The other aircraft, Viper 1, and its two pilots on board landed safely at Essendon Airport after making a mayday call.
In its final report into the crash, the Australian Transport Safety Bureau (ATSB) confirmed the fateful manoeuvre Viper 1 rolling inverted before Viper 2 passed directly under it.
Following a first attempt, Mr Gale advised it provided a "good filming opportunity" and the pilots decided to repeat the move after discussing it over the radio.
"This specific manoeuvre had not been briefed before the flight and increased the risk of collision," the report reads.
"A subsequent in-flight discussion of the manoeuvre did not allow for full consideration of associated risks before a second attempt was commenced."
The right wings of the jets collided during the second attempt when Mr Gale pitched up and banked left, away from Viper 1.
Viper 2 sustained "substantial damage", immediately losing of control and hitting the water at high speed.
ATSB Chief Commissioner Angus Mitchell said pre-briefing of in-flight manoeuvres was critical to safe formation flying to mitigate the risks of increased pilot workload and distraction.
"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," he said.
The ATSB investigation found Jetworks Aviation, Mr Gale's Essendon Fields-based business, did not hold the required certificate to film flights and the S-211s were not legally permitted to be used for that purpose.
The surviving pilot did not follow medical restriction requirements to operate aircraft with a side-by-side seating configuration and a type-qualified safety pilot.
These factors did not directly contribute to the crash but operating outside of the limits removed in-built safety defences and structures designed to identify and mitigate risks, Mr Mitchell said.
Neither aircraft was fitted with a flight data recorder or cockpit voice recorder but the crash was captured on cameras fitted to Viper 1.
Footage from Mr Rose's hand-held camera and others mounted in the cockpit of Viper 2 were not found in the wreckage.
The TV series being filmed was set to show a "group of high achievers" attempting to master flying, aerobatics and formation, with Australian comedian Tommy Little among the "student pilots" featured.
