A plane crash that killed a Victorian teenager on her first solo training flight was likely to have occurred after she manipulated the controls while on autopilot.
The 19-year-old died when her single-engine Cessna aircraft departed Point Cook Airport and crashed into a hill at Millbrook, near Ballarat on September 8, 2015.
An Australian Transport Safety Bureau investigation on Tuesday found it was likely the student pilot manually manipulated the controls, while the autopilot was on, and engaged in a vertical mode.
This caused the plane to rapidly descend from a low height, and with rising terrain in front the RMIT aviation student had limited time to recover before impact.
The ATSB found the student may have been unaware of exactly how the autopilot functioned.
As a result, it has issued safety recommendations to the aircraft and autopilot manufacturers to provide cautions and warnings for autopilot systems.
The flight training organisation has also updated its operations manual to include warnings about the operation and function of the autopilot systems - warnings absent in the manufacturer's documentation.
"This accident highlights how essential it is for all pilots to develop a thorough understanding of all systems fitted to the aircraft they are flying," the ATSB said in its report.
"Pilots should be aware that if automation is not performing as expected, then the safest option under most circumstances is to disengage the system and manually fly the aircraft."