Transport safety investigators have recommended additional checks be made of ATR turboprop aircraft which fly from Canberra to Sydney and some regional routes following a potentially "catastrophic" incident in 2014.
The Australian Transport Safety Bureau made the recommendation in its second interim report into a Virgin Australia flight from Canberra to Sydney on February 20, 2014.
The ATR72 aircraft sustained a "pitch disconnect" while descending into Sydney when the left and right elevator control systems uncoupled.
Pilots noticed the airspeed rising higher than expected. The first officer reduced engine power and used touch control steering to temporarily disconnect the autopilot before manually raising the nose to control the speed.
The captain was unsure if the first officer's control inputs were enough to avoid over-speeding. He put one of his hands on the controls and disconnected the autopilot to raise the nose higher.
Shortly afterwards, concerned about the high nose-up position, the first officer put his hands back on the controls.
A pitch disconnect warning was triggered, which enabled independent movement of the left and right elevator controls by both pilots.
"The aerodynamic loads generated during the pitch disconnect resulted in serious injury to the senior cabin crew member and significant damage to the aircraft's horizontal stabiliser."
The report says the load exceeded design strength requirements and had potential to "result in catastrophic damage" and a subsequent loss of control.
Virgin and Toll Aviation are the operators of ATR aircraft in Australia.
ATSB chief commissioner Greg Hood said that following investigations, the bureau had issued safety recommendations to the aircraft manufacturer [ATR], the European aviation safety regulator [EASA] and the Civil Aviation Safety Authority [CASA].
"Since we identified this issue, our aeronautical and structural engineers have conducted extensive analysis based on additional data provided by ATR," he said.
"The findings of that analysis, supported by an independent peer review from the UK Air Accidents Investigation Branch, confirmed our initial concerns."
Mr Hood welcomed action taken by Virgin and Toll to reduce the risk of another incident and to manage adverse outcomes if one should occur.
A spokesman for Virgin Australia said safety was the airline's highest priority.
"We continue to liaise closely with the relevant regulatory bodies and the aircraft manufacturer in relation to the ongoing investigation into the ATR's pitch disconnect mechanism," the spokesman said.
Virgin recently announced it's reducing the number of turboprops in its fleet from 14 to six as part of an "optimisation program" but the spokesman said this was not related to the safety investigation.
It's understood turboprop operations will be consolidated to the ACT, NSW and Victoria.
The ATSB recommended ATR determine as soon as possible if the aircraft can safely withstand the aerodynamic loads resulting from a pitch disconnect.
In the event of an adverse finding, it recommended ATR take "immediate action to ensure the ongoing safe operation of the aircraft".
A spokesman for CASA said the agency had been closely monitoring the investigation.
"CASA continues to audit ATR aircraft operators to ensure appropriate actions have been taken to reduce the likelihood of the aircraft being mishandled in a manner similar to the incident flight," the spokesman said.
"Flight procedures and pilot refresher training for the ATR aircraft operated in Australia have been amended since the event occurred.
"CASA will look carefully at the findings of the aircraft manufacturer's engineering analysis of the issues associated with a pitch disconnect when this work is completed.
"If this analysis raises any ongoing safety issues CASA will take appropriate action."
CASA requires monthly reports from Virgin and Toll.
A spokesman for ATR said the aircraft manufacturer was completing an assessment of transient elevator deflections.
"ATR continues to provide assistance to the safety investigation conducted by the ATSB," the spokesman said.
