The Australian Transport Safety Bureau on Thursday released the early findings into its probe of the Regional Express propeller shearing which occurred during a flight from Albury to Sydney on March 17.

Its report revealed a fatigue fracture had been found in the propeller mounting flange –the equipment that attaches the propeller to the gearbox – and that defect had continued into the propeller shaft.

The inspection at the ATSB’s site in Canberra also found corrosion near where the fracture began.

ATSB chief commissioner Greg Hood said the scenario had not occurred previously.

“This is the first known critical failure of this type, initiating within the propeller hub flange of the GE Aviation CT7-9B engine,” Mr Hood said.

“Both the operator and the engine manufacturer have already taken proactive safety action in response to the ATSB’s safety advisory notice.

“GE Aviation is conducting metallurgical analysis on the propeller flange and hardware at its laboratories in Cincinnati, USA.

“They are also inspecting additional propeller gearboxes and reminding all operators to follow maintenance and inspection procedures.

“GE Aviation will release additional maintenance and inspection recommendations if they become necessary.

“Regional Express has quarantined all propeller gearboxes with propeller shafts of the same series as that installed in the aircraft involved in the incident.”

The ATSB’s continuing investigation will focus on maintenance procedures associated with the propeller gear box shaft and examine factors that may have contributed to the fatigue fracture at the propeller mounting flange.

During the flight, crew shut down the right-hand engine following "abnormal indications" with the pilot "feathering" the propeller to reduce drag.

It was at this point that the propeller assembly separated and rotated upwards and to the right of the aircraft - luckily avoiding contact with the plane which was carrying 16 passengers and three crew.

Wagga City Aero Club flying captain John Smith said on a normal day, engine failure would barely be worth mentioning.

“[A propeller falling mid-flight is] not good at all… but it’s very, very rare,” Mr Smith said. “It was certainly no danger to any passengers.”

Mr Smith said it is more of a problem when a propeller becomes stationary.