A Queensland coroner has been unable to determine why a pilot lost control and crashed into seawater at the Gold Coast in 2019, causing his death and that of his female passenger.
Following a three-day inquest into the deaths in December, Coroner Carol Lee on Tuesday recommended a review of training requirements for aerobatic pilots and the safety regulations for the Soviet-era military training aircraft involved in the crash.
On the morning of June 5, 2019, 52-year-old pilot Martinus Van Hattem was hired to use the aircraft he owned, a YAK model 52 with a single propeller engine, to take Trista-Lea Applebee for a private scenic flight involving "low-level" aerobatic manoeuvres.
Ms Lee found Mr Van Hattem and Ms Applebee died as a result of a high-speed impact with the sea but on the available evidence could not find that adverse weather, a lack of fuel or mechanical issues had contributed.
Ms Lee also found Mr Van Hattem did not have any significant medical or mental health issues and was "fit to fly" but his ability to avoid a crash could have been impaired by a loose object interfering with the aircraft's controls during inverted flight.
"I express my sincere condolences for the losses that each of the (Van Hattem and Applebee) families have suffered and hope that the investigation and this inquest has provided some answers," Ms Lee stated.
"It is hoped that improvements will be made to this aspect of the aviation industry to prevent deaths occurring in similar circumstances in the future."
Ms Applebee's friend had purchased the flight for $200 as a gift for her 31st birthday.
Mr Van Hattem took off in the YAK 52 from Southport Airport with Ms Applebee as his passenger at 9.46am.
The aircraft was last seen on radar over South Stradbroke Island at or above 1200 feet.
When the aircraft failed to return to the airport, four helicopters began to search the area and wreckage was spotted in the surf break on the eastern side of South Stradbroke Island at 4.30pm.
Mr Van Hattem's body was found the next day entangled in wreckage and Ms Applebee's body was spotted on June 7 off North Stradbroke Island.
Ms Applebee borrowed her friend's phone to take photos during the flight but the handset was never recovered.
Mr Van Hattem's YAK 52, which was built in Romania in 1982 and registered in Australia in 2017, was not required to carry a 'black box' cockpit recorder.
"Witnesses ... did not hear or see anything about the performance of the aircraft that would indicate that the aircraft was malfunctioning," Ms Lee stated in her findings.
The Australian Transport Safety Bureau noted UK authorities ordered more safety checks for YAK 52s after one of the aircraft was involved in a fatal crash in Russia in 2010.
Ms Lee recommended that the Civil Aviation Safety Authority consider "a minimum period or duration of training and instruction" for pilots intending to fly aerobatic manoeuvres and review safety standards around 'warbird' vintage military aircraft.
Ms Lee also recommended that CASA assess the risks posed by loose objects inside a YAK 52 during aerobatic manoeuvres.
