A passenger plane landed safely Friday after one of its two propellers fell off in an extraordinary emergency as it approached Sydney Airport.

The Regional Express Airlines crew reported the right engine propeller assembly separated from the Saab 340 airliner 12 miles southwest of the airport, Civil Aviation Safety Authority spokesman Peter Gibson said.

Flight 768 was carrying 16 passengers and three crew from Albury, 300 miles southwest of Sydney. Accident investigators have appealed to anyone who finds propeller parts on Sydney's outskirts to come forward to help explain what went wrong, Gibson said.

"Not just the propeller, but the shaft that connects it into the engine have all come off and the assembly has fallen away to the ground," Gibson said.

"This is very, very, very unusual. It happens very, very rarely," he added. "They were lucky."

The parts that fell off apparently did not cause further damage to the plane.

One of the two pilots made a pan pan call. That indicates an urgent situation that is not immediately life-threatening but requires assistance from the ground. Pan pan indicates a lesser emergency than a mayday alert.

"Our propeller has just sheared off but normal controls. Still able to fly," a pilot said in a radio call broadcast by media.

The Sydney-based airline said in a statement that the crew had followed standard operating procedures and the plane had landed "normally and on time."