Rex flight ZL768 lost one of its two propellers 20 kilometres out of Sydney last week.

Civil Aviation Safety Authority spokesman Peter Gibson said it was extremely rare for propellers on large passengers planes to separate from the engine.

“You have to go back to 1991 in the United States, and you have to go back to the 1960s for anything like this in Australia,” he said.

He said commercial pilots trained regularly for engine failures and said Rex’s two pilots were “remarkably composed” given the unusual circumstances.

“They’re trained to handle engine failures, but not in their wildest dreams would they expect a propeller to fall off,” Mr Gibson said.

He said during engine failures, pilots were trained to compensate for a propeller that wasn’t moving.

“When something like this happens, that’s where the importance of the Australian Transport Safety Bureau investigation is, they’ll look at this in great detail,” Mr Gibson said.

“In time, they’ll produce a detailed report and from that, we’ll look to see if there’s any safety lessons.”

Rex has taken five out of service since the incident.

“Rex has 55 Saab 340 aircraft in the fleet,” Rex spokeswoman Alicia Chapple said.

“We currently have a total of five aircraft out of service (in addition to the aircraft involved in Friday’s event) as part of the ongoing investigation.

“Two are Pel-Air freighters.  Of the remaining three, one is from the Sydney network and two are from the Melbourne network.  We are unable to pinpoint the direct impact on particular routes.”