Authorities in Papua New Guinea say the pilot of a doomed Airlines PNG flight reported no problems as she came in to land near Kokoda.

Authorities have released an interim report into the plane crash that killed 13 people, including nine Australians, near Kokoda last month.

The report only outlines the factual circumstances surrounding the crash and does not identify a cause.

It says the last communication received from the Airlines PNG flight was a message from pilot Jannie Moala saying she had begun her descent into Kokoda.

There was extensive low cloud in the area at the time, with thunder storms and associated turbulence.

The report says both the pilot and first officer were appropriately qualified and had extensive experience flying in the Twin Otter plane.

Flight instruments have been sent to Canberra for examination and the plane's engine will soon be sent to Canada.

A final report is expected in around six months' time.