The two men on board the Diamond DA42 faced "a very peculiar emergency at a very crucial stage" as the aircraft took off from Adelaide's Parafield Airport on April 29, the Australian Transport Safety Bureau said in a preliminary report.
An actuator rod had fractured into two pieces, meaning the nose landing gear remained extended during the 42-second flight, chief commissioner Angus Mitchell said.
"The failure … is known to have caused in-flight controllability issues with this aircraft type in the past," he said on Tuesday.
"(It) is one of a number of scenarios, including loss of engine power in one engine, that the investigation is examining."
Flight instructor Robert Hoyle, 29, and his 24-year-old student died when the aircraft crashed into the Flight Training Adelaide hangar at Parafield Airport, causing a fire that injured nine people and destroyed several other aircraft.
Mr Hoyle's father, Scott Hoyle, said his family "remains heartbroken by the loss of our beloved Robert".
"Whilst we take some comfort in the confirmation that the accident appears to have been caused by mechanical error, it does not lessen our grief," he said.
"Robert dedicated his life to aviation and we trust that the full findings of the ATSB's investigation, when announced, will serve as his lasting and final contribution to the industry he loved so much, by helping to ensure that such a tragic event is never repeated."
The ATSB has released a safety notice about the issue, which has "international ramifications" for 600 similar aircraft worldwide.
Mr Hoyle and the trainee, who had recently gained his commercial pilot's licence, had planned to conduct simulated engine failure circuits.
CCTV footage shows that after the aircraft took off, it deviated left, was realigned with the runway, and then began veering left.
The main landing gear was retracted but the nose landing gear remained extended.
"Notably, 27 seconds after getting airborne, the pilot instructor made an emergency engine failure radio call," Mr Mitchell said.
"No further radio calls were heard from either pilot."
As the instructor and trainee tried to resolve the emergency, the potential for cognitive overload "would have been very real", he said.
The fractured rod had "the potential to interfere with rudder controls", but the situation "probably looked more like engine failure" to the pilots, Mr Mitchell said.
The left engine was not operating when the plane crashed moments later, investigators found.
The aircraft manufacturer had issued bulletins in 2013 and 2019, after separate incidents involving the fractured part, including one where a pilot was able to regain control after re-extending the landing gear.
Metallurgical analysis of the broken rod was ongoing, but a preliminary examination had found "indications of fatigue cracking prior to complete failure of the component".
The ATSB had issued a safety advisory notice because of the failure of a critical aircraft component and its potential to lead to a loss of control, and the fact that many similar aircraft are used for flight training.
Its final report is expected to be completed in about 18 months.
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