A Black Hawk helicopter has made a forced landing north-west of Sydney after sending out a distress call just after 7pm on Wednesday.
The helicopter, believed to be from the Richmond RAAF base, sent out a pan-pan alert just before it landed in a field at Wisemans Ferry.
A pan-pan alert signals a matter of urgency on an aircraft but is , one step below mayday given there is no immediate danger to life.
Initially the alert, broadcast to all aircraft in the area, said the helicopter was coming down in a field between Richmond and Prospect.
But a spokeswoman for the Department of Defence confirmed the craft landed to the city's north.
"A Black Hawk has had a precautionary landing at Wisemans Ferry," the spokeswoman said.
"A warning light came on, and as soon as that light came on, they had to land."
No further detail was immediately available.
A spokesman for the Australian Transport Safety Bureau said they had not been told of the forced landing.
"But there's no requirement for Defence aircraft to inform the ATSB of an incident," the spokesman said.
Earlier this year, one US soldier was killed and two were injured when a MH-60 Black Hawk made a "hard landing" in the US state of Georgia.
In 2006, an Australian Black Hawk helicopter crashed onto HMAS Kanimbla in Fiji, killing two Australian servicemen.
In 1996, two Black Hawk helicopters collided near Townsville, killing 18 soldiers.