Late last week passengers on a Regional Express aircraft flying from Albury to Sydney endured a nightmare flight after one of the propellers sheared off mid-flight, forcing pilots to make an emergency landing.

On Tuesday, a NSW Police helicopter patrolling Sydney's south-west spotted the propeller in bushland at Revesby.

A crime scene has been set up at the location where the propeller was found in the Georges River National Park, just off The River Road.

The site is within a few kilometres of suburban homes, and demonstrates how fortunate it was that no one was seriously injured or killed when it fell from the plane.

The 34-seat plane, carrying 16 passengers and three crew, was about 19 kilometres from Sydney Airport when its right-hand propeller flew off, narrowly avoiding hitting the wing and tail.

The two pilots on board flight ZL-768 from Albury were forced to declare a PAN, which is one step down from a full-scale Mayday, before safely landing at the airport.

"Police are now working with the Australian Transport Safety Bureau to safely recover the item as inquiries into Friday's incident continue," a police spokesperson confirmed.

The propeller will form a key part of the ATSB's investigation into what caused it to break off at the shaft of the Saab 340's right-hand engine.

The ATSB said the location of the propeller in bushland was broadly consistent with its calculations. Investigators had been calculating the likely trajectory of the propeller using data from the plane's flight data recorder.

"The ATSB investigation team will examine the propeller assembly to determine the contributing factors that led to its detachment from the aircraft," it said.

The Saab 340 aircraft's first officer saw the propeller break away, and rotate upwards and to the right before moving in a horizontal direction.

Aviation watchers have said it was "incredibly lucky" the propeller did not hit the wing, fuselage or the tail, which could have been catastrophic for the aircraft and those on board.

In the wake of the incident, Regional Express has temporarily grounded five aircraft to allow engineers to remove propeller gear boxes and shafts similar to those on the Saab 340 forced to make an emergency landing.