A light aircraft that crashed near Canberra last year, killing the two men on board, did so because of its slow speed and angled turn, a safety investigation has suggested.
The pilot, aged 31, and his passenger, 18, had been inspecting powerlines during their three-hour flight on April 13, 2021.
Witnesses saw the plane plummet and crash at about 4:30pm just north of Sutton, a New South Wales village near the ACT border.
One witness told the ABC that the aircraft, a Cessna 172 owned by Oberon Aviation Services, was spinning before it hit the ground.
The impact killed the men and destroyed the plane.
An Australian Transport Safety Bureau (ATSB) analysis of the incident released today suggested the plane was flying too slowly for the steep turn the pilot was attempting.
Flight data and witness accounts indicate the plane banked sharply to the left just before the wing stalled.
The ATSB report said investigators "estimated that the final turn was likely conducted at a comparatively high angle of bank and closer to the stall speed of the aircraft".
"As the manoeuvre continued, the aircraft likely exceeded the critical angle of attack for the wing, causing the wing to aerodynamically stall," it said.
The plane was too low to the ground when it stalled for the pilot to recover control, the ATSB found.
Investigators considered whether the pilot's final manoeuvre was an attempt to evade birdlife, but found "insufficient evidence to determine if that may have influenced the turn".
It was also possible the aircraft hit turbulence just before its final turn, though the wind was light at the time.
ATSB's transport safety director, Stuart Macleod, said the investigation reinforced to pilots "the importance of managing airspeed and bank angle to minimise the risk of stalling".
"This is particularly important when operating in close proximity to the ground, such as conducting low-level air work, as well as during take-off and landing, as recovery may not be possible."
The findings did not apportion blame to the pilot or the operating business.
Oberon Aviation Services has since amended its operations to include further training for pilots who carry out low-altitude surveys of powerlines.
