An investigation is underway after the a propeller sheared off a plane, carrying 16 passengers and three crew mid-flight on Friday, March 17. 

The aircraft landed safely in Sydney despite the detachment and it is believed no one was harmed from the fall of the rogue propeller, which is yet to be located in the Camden area. 

 REX announced it would ground five planes of the same series and quarantine the propeller gear boxes and shafts for further testing. 

In a decision it described as due to an "abundance of caution", Regional Express said the gear boxes and shafts of the same series would be immediately removed from service while it waited for air-safety investigators to "determine the root cause of the incident".

The airline said the disruption was expected to cause minor service delays for two-to-three days.

Regional Express chief operating officer Neville Howell said the separation of the propeller from the engine was an "extremely rare event", and the only other similar recorded incident occurred to a plane operated by US airline Comair in 1991.

"The crew demonstrated enormous composure and discipline under extraordinary circumstances," he said on Monday.

"The captain displayed exceptional skills in landing the aircraft so smoothly in bad weather and strong winds, so much so that the passengers did not notice anything different."

The airline said investigations over the past three days had found the propeller sheared off at the shaft, leaving intact all the fittings at the main assembly.

Investigations thus far have found Flight ZL768 – tracking from Albury to Sydney – experienced engine trouble 25 kilometers south-west of its destination. 

The engine was shut down and the propeller feathered to reduce drag. 

The prop then rotated upwards and horizontally away from the plane.

The propeller has yet to be found, and the Australian Transport Safety Bureau has advised anyone who finds it to leave it where it is, and contact its investigators or the police.