The very first flight by Batik Air from Bali to Canberra arrived in darkness before the traffic control tower had started operating for the day. The result was a series of failures to communicate clearly between the pilot and people on the ground as the plane flew below safety limits.
These are the preliminary findings of the official investigation by the official Air Transport Safety Board.
"Forecast tailwinds resulted in an estimated arrival time just prior to 0600 on 14 June, which was earlier than planned, and before Canberra Tower and Canberra Approach air traffic control commenced services for the day," the ATSB said.
As the shift at the Canberra tower started on June 14, the unusually low flight path of the Batik Boeing 737-800 was noticed from the ground.
One of the results of the early arrival of the flight from the Bali airport, Denpasar, was then a series of failures to communicate clearly between the pilot on the aircraft and people on the ground in Canberra.
The ATSB report details a series of attempts to contact the aircraft directly and via controllers in Melbourne.
The aircraft went into a holding pattern around Canberra Airport, flying at one stage over the "restricted area" of the Deep Space Communications Complex at Tidbinbilla to the west of Canberra.
"During this holding pattern, the aircraft levelled out at 4,700 feet, but this meant it descended below minimum holding altitude of 5,600 feet, and at one point the aircraft passed 924 feet above terrain," ATSB Chief Commissioner Angus Mitchell said.
Mr Mitchell said that at one stage the crew "became uncertain as to whether the aircraft would be operating within, or outside of, controlled airspace during the standard arrival route and approach".
Inspectors from the ATSB have interviewed crew members and people at Canberra's air-traffic control.
The ATSB noted that Batik Air had since improved its briefings to pilots of flights to Canberra, and rescheduled flights so they don't arrive before 6am.
"A final report with analysis and findings will be released at the conclusion of the investigation, but we note the operator has already pro-actively taken safety actions," Mr Mitchell said.
"These include revising their Canberra Airport briefing documentation, issuing flight crew notices highlighting procedures for operating in non-controlled airspace, and rescheduling flights to Canberra to ensure they arrive during air traffic control operating hours."
Batik Air is part of the Lion Air Group which also has airlines in Thailand, Indonesia and Malaysia. It operates three direct flights a week between Canberra and Bali.
The Batik Air incident came almost 20 years after another serious incident, that time involving a Qantas flight inbound from Perth in the early hours of July 14, 2004.
In that incident, the control tower at Canberra Airport had been unmanned because of "staffing issues".
