The hunt is on for a propeller that fell off a regional passenger plane as it approached Sydney Airport.
The right propeller fell off the Regional Express Saab 340 on Friday when it was approaching the airport, the Australian Transport Safety Bureau says.
The flight from Albury, carrying 16 passengers and three crew, subsequently performed a safe emergency landing in Sydney after midday.
"The ATSB urges anyone who finds a piece of suspected aircraft debris not to handle it," the bureau said in a statement.
Instead, Sydneysiders are encouraged to call local police or the ATSB direct.
The crew made a distress call stating the propeller assembly had "dislodged" when the plane was about 20 kilometres from Sydney Airport, the Civil Aviation Safety Authority says.
AAP understands the propeller broke off over the Camden area, southwest of Sydney.
That's despite the ATSB in its statement referring to a malfunction "19km NW of Sydney Airport".
Flightradar24 shows Rex flight 768 heading over Camden before passing over the airport, doing a loop over Sydney's north and Ku-ring-gai Chase National Park, and then returning to land safely.
CASA spokesman Peter Gibson said in his 20 years in the aviation industry he's never heard of a propeller falling off a plane.
"I've never come across it ... it's very unusual," he told AAP.
Rex on Friday said the crew followed standard operating procedures after the propeller fell off "and the aircraft landed normally and on time at Sydney Airport".
"The passengers and crew members were met by Rex staff upon arrival and did not require any further assistance," the company said in a statement.
The ATSB has deployed a team of three investigators with expertise in materials failure engineering, recorded flight data analysis and human factors.
"Over the next few days, investigators will examine the aircraft, interview the flight and cabin crew, and collect maintenance records and recorded flight data," the bureau said.
Regional Express operates a fleet of more than 50 Saab 340 aircraft on about 1500 weekly flights to 58 destinations across Australia.
© AAP 2017Image credit: Bidgee [CC BY-SA 3.0 au (http://creativecommons.org/licenses/by-sa/3.0/au/deed.en)], via Wikimedia Commons