The Viscount 832 aircraft VH-RMI was a low wing monoplane constructed in 1958-59 by Vickers Armstrong Aircraft Limited, England, known as The British Aircraft Corporation, Weybridge Division (referred to as B.A.C.), for passenger and freight carrying. The type number 832 indicates that it was one of the 810 series aircraft manufactured specifically for Ansett-A.N.A.
At the time of the accident VH-RMI was fitted to accommodate 63 passengers. It was designed to be operated by a flight crew of two pilots and cabin staff. The aircraft had not been involved in any previous accident reported to the Department of Civil Aviation.
The aircraft was operating.under a current Certificate of Registration issued by the Department of Civil Aviation No. 3253. The Certificate was issued on the 14th February, 1961, to remain valid until the 13th February, 1970 and there was also a current Certificate of Airworthiness for the aircraft which was last renewed on the 10th April, 1964 to remain valid until the 10th April, 1973, subject to the aircraft continuing to be operated and maintained in accordance with the Air Navigation Regulations and Orders and the approved maintenance system.
The accident occurred while the aircraft was on a scheduled public transport passenger flight from Mt. Isa to Longreach, a distance of 316 nautical miles.
The aircraft departed from Mt. Isa at 1208 hours E. S. T. on 22nd September 1966 on Flight 149. It was cleared to proceed in accordance with the terms of the flight plan prepared and approved before departure from Mt. Isa which, as already appears, indicated it would take 73 minutes to fly to Longreach and would cruise at a height of approximately 17,500 feet.
Evidence obtained from the flight data recorder indicates that the aircraft reached this flight level at approximately 1240 hours and that it continued at this level with the automatic pilot engaged until 1247 hours. In normal circumstances the aircraft would have continued at its cruising flight level with the automatic pilot engaged until approximately 1305 hours when it would have been 70 miles from Longreach in a position to commence a normal descent for landing. However indications from the flight data recorder showed that the automatic pilot was disengaged prematurely at 1247 hours and this was followed shortly after by a descent which was described in a message from the aircraft to Longreach as an emergency descent. It would seem therefore that disengagement of the automatic pilot perhaps signifies the point of time when an emergency situation became apparent to the crew.
A series of messages between the aircraft and Longreach and other aircraft indicate the nature of the emergency as it became manifest to the crew.