Investigators say a mechanical failure that blew a hole in the engine of a Qantas jet headed to Sydney from San Francisco also caused damage to the plane's wing flaps.
The engine failure early Tuesday forced the plane to return to the airport shortly after takeoff.
Investigators from the Australian Transportation Safety Board arrived in San Francisco Thursday to examine the engine and determine the cause of the incident.
The board said in a statement that the failure led "ejected material" to puncture a hole in the engine's outer covering and damage the flaps. The engine will be shipped to a Hong Kong maintenance facility for further examination.
The plane made an emergency landing at San Francisco International airport without further difficulty.
No one was injured.