A plane nosedived during an aerobatic manoeuvre because a restraint harness failed, causing the pilot to fall out of his seat, an investigation has found.
The incident occurred 30 minutes after a CAP 10B aerobatic aircraft, operated by Flight Training Adelaide, took off from Adelaide's Parafield Airport in February.
In an unrelated incident in April, another aircraft operated by the company crashed into a hangar at the same airport, killing an instructor and trainee pilot.
The Australian Transport Safety Bureau on Tuesday released a report on the February 4 incident, which occurred when an instructor and student pilot were conducting an upset prevention and recovery training flight.
The plane was at an altitude of about 7000 feet when the instructor's crotch strap suddenly released as they were rolling the aircraft into an inverted position during a split S manoeuvre, it said.
"As a result of the strap disconnection, the instructor fell out of their seat, impacting the overhead canopy and briefly releasing pressure on the flight control stick," ATSB director of transport safety Kerri Hughes said.
"With the aircraft in a nosedive with airspeed increasing, the instructor reported they completed a pitch roll to the left, and gently pulled out to ease out of the dive, recovering to normal flight."
The aircraft recovered at 3000 feet and returned to Parafield without further incident.
As a result of hitting the canopy, which sustained minor damage, the instructor received a minor head injury.
Pre-flight safety checks on the harness by the instructor did not identify any issues, but the ATSB investigation found evidence of wear on the buckle's internal sub-parts and latches.
The investigation found the manufacturer's inspection method did not guarantee that deterioration in the buckle would be detected, and the restraint's five-year service life did not account for use in some aerobatic training.
The restraint manufacturer, Schroth, would amend its prescribed service life when used during aerobatic flight and Flight Training Adelaide has limited the use of the harness to three years, or 1000 hours.
On April 29, FTA flight instructor Robert Hoyle and a trainee pilot were killed and nine others were injured after a nose landing gear component failed as a plane took off and crashed into a hangar at Parafield.
An actuator rod fractured into two pieces, meaning the nose landing gear remained extended during the 42-second flight, a preliminary ATSB report found.