Fatigue fracture led to Rex propeller fall

A preliminary report on how a propeller detached from a Regional Express aircraft near Sydney Airport in March has found a fatigue fracture caused the failure.

An investigation has found a "fatigue fracture" caused a propeller to fall off a regional aircraft. (AAP)

A Regional Express aircraft propeller that detached mid-flight on its way to Sydney last month came off because of a "fatigue fracture", an investigation has found.

The Australian Transport Safety Bureau on Thursday released an initial report into the March 17 mishap on the Albury to Sydney afternoon flight, saying the fracture started in the propeller mounting flange - the part that attaches the propeller to the gearbox - before continuing to the propeller shaft.

"This is the first known critical failure of this type, initiating within the propeller hub flange of the GE Aviation CT7-9B engine," ATSB chief commissioner Greg Hood said in a statement.