Investigators have not been able to find the cause of a plane crash off Queensland's Moreton Island two years ago that claimed the lives of a couple on a scenic flight.
A search was launched for the 70-year-old male pilot and his 52-year-old wife when they made a mayday call from their hired plane and lost contact with flight controllers on January 22, 2020.
The couple were never found but the Australian Maritime Safety Authority eventually called off the search, saying the crash "would not have been survivable".
The wreckage of the Cessna 182 light aircraft was found a week after the crash on the ocean floor 30m below sea level.
However, Australian Transport Safety Bureau (ATSB) could not determine the cause of the crash after examining the aircraft, saying in a report tabled on Thursday that there was "no evidence of pre-impact defects or structural failure".
The ATSB says it could not find any "pre-existing defects with the engine or aircraft systems" that would have caused engine failure and discovered the aircraft still had 135 litres of fuel left, which was "sufficient" for a successful return.
"The ATSB examination of the underwater video identified that the aircraft was likely destroyed by collision with water at a moderately high speed," the report says.
"Damage to the aircraft cabin from the collision with water indicated that it was unlikely to be survivable. There was no evidence of fire."
ATSB Transport Safety director Mike Walker said the engine's power was reducing before the plane crashed into the sea near Flinders Reef.
He said it indicated an ice build-up on the engine which is common in the region.
"However, a conclusion regarding the possible influence of carburettor icing on the development of the accident could not be drawn with any certainty," Dr Walker said.
The investigation did find that the aircraft had maintained a course away from suitable landing areas at a speed not ideal for the plane to successfully glide back to land in an emergency.
"The ATSB also found that the pilot had descended over water beyond the glide range of a suitable landing area twice on a previous flight, limiting the options for a forced landing in the event of an emergency," the report says.
"Although it could not be determined whether the aircraft's descent out of glide range was intentional, pilots are reminded that the operation of single-engine aircraft over water should at all times be conducted with consideration of the aircraft's glide distance to a suitable landing area."
