On Sunday 10 March 1946 a Douglas DC-3 aircraft departed from Hobart, Tasmania, for a flight to Melbourne, Australia. The aircraft crashed into the sea with both engines operating less than 2 minutes after takeoff. All twenty-five people on board the aircraft died. It was Australia's worst civil aviation accident at the time."Air Liner Hit Water At A Great Speed" The Canberra Times – 12 March 1946, p. 2 (National Library of Australia) Retrieved 15 September 2011
An investigation panel was promptly established to investigate the accident. The panel was unable to conclusively establish the cause but it decided the most likely cause was that the automatic pilot was inadvertently engaged shortly after takeoff while the gyroscope was caged. The Department of Civil Aviation took action to ensure that operation of the automatic pilot on-off control on Douglas DC-3 aircraft was made distinctive from operation of any other control in the cockpit, and that instructions were issued impressing on pilots that gyroscopes should be un-caged prior to takeoff.
An inquiry chaired by a Supreme Court judge closely examined three different theories but found there was insufficient evidence to determine any one of them as the cause. This inquiry discovered that the captain of the aircraft was diabetic and had kept it secret from both his employer and the Department of Civil Aviation. The judge considered the captain's diabetes and self-administration of insulin probably contributed significantly to the accident but he stopped short of making this his official conclusion.
In his report, the judge recommended modification of the lever actuating the automatic pilot. The inquiry uncovered four irregularities in the regulation of civil aviation in Australia and the judge made four recommendations to deal with these irregularities.
The flight The Australian National Airways aircraft registered VH-AET arrived at Cambridge aerodrome at 8:15 pm local time, about four hours late. The return flight to Essendon Airport was scheduled to depart at 4:50 pm, but did not do so until 8:50 pm."Airliner Crashes Into Sea" The Mercury – 11 March 1946, p. 1 (National Library of Australia) Retrieved 14 September 2011
On board were 21 passengers, 3 pilots and an air hostess. Douglas DC-3 (and C-47) aircraft were normally crewed by two pilots but on 10 March the cockpit of VH-AET was occupied by a third person, a supernumerary pilot who was making his first flights with the airline."Seven Bodies Of Air Crash Victims Recovered" The Sydney Morning Herald – 12 March 1946, p. 1 (National Library of Australia) Retrieved 21 September 2011"Likely Effect Of Bird On Speed" The Mercury – 3 May 1946, p. 9 (National Library of Australia) Retrieved 1 October 2011 The weight of the aircraft was about below the maximum authorised weight."Plane Disaster" The West Australian – 3 May 1946, p. 10 (National Library of Australia) Retrieved 27 September 2011 The takeoff was into a light southerly wind towards Frederick Henry Bay and the sea. Observers at the aerodrome reported that the takeoff was normal, and both engines were operating perfectly.
Witnesses in the vicinity of Seven-Mile Beach estimated that the aircraft reached a height of a little above "Gannet May Have Caused Plane Disaster" The Advocate – 2 May 1946, p. 5 (National Library of Australia) Retrieved 25 September 2011 before turning left slightly and descending steeply. The aircraft cleared the land and crashed into Frederick Henry Bay about beyond the water's edge and a mile (1.6 km) from the western end of Seven-Mile Beach."Open Finding On Victims Of Air Crash" The Mercury – 26 July 1946, p. 9 (National Library of Australia) Retrieved 15 September 2011 After takeoff it flew for less than 2 minutes"Thinks Air Crash Due To Personal Factor" The Advocate – 1 May 1946, p. 5 (National Library of Australia) Retrieved 25 September 2011 and covered a distance of only .
Recovery
Wreckage
On learning of the crash at nearby Seven-Mile Beach employees of Australian National Airways raced from Cambridge aerodrome to lend assistance. About 11:15 pm the rear fuselage came to the surface a short distance off-shore. Donald Butler, one of the employees, feared the air hostess might still be trapped in her seat in the rear of the fuselage. He took a length of rope, swam out to the floating piece of structure, attached the rope to the tailwheel and then swam back to the beach. A motor lorry was used to drag the rear fuselage ashore but there was no-one inside. The right tailplane, elevator and trim tab were almost undamaged. The elevator trim tab was still set appropriately for a shallow climb after take-off.
The wreckage was in about of water."Three More Bodies Washed Up From Airliner Crash" The Canberra Times – 13 March 1946, p. 1 (National Library of Australia) Retrieved 19 September 2011 A diving pontoon was towed to the site by Royal Australian Navy ship HMAS Huon. Diver Glen Thorne found pieces of wreckage scattered over a wide area of the sea bed. The aircraft had disintegrated and there were few recognisable pieces of structure. Key parts of the wreckage were eventually recovered from the sea bed by Thorne working from the pontoon."Wreckage Of Airliner Found By Diver" The Mercury – 14 March 1946, p. 13 (National Library of Australia) Retrieved 22 September 2011
Bodies About 4 hours after the crash the mutilated body of a woman was washed onto Seven-Mile Beach. Fifteen minutes later the body of a man was washed ashore. It was later identified as the body of the captain. At intervals until 6:30 am another 5 bodies were washed ashore. The next day, another 3 bodies were recovered. The bodies were badly mutilated and either naked or clad only in vestiges of underclothing, indicating the severity of the impact with the water. One body was missing a leg. A head, severed from its body, was recovered in the vicinity."Fire Theory In Airliner Crash" The Argus – 13 March 1946, p. 3 (National Library of Australia) Retrieved 22 September 2011
The bodies of 21 of the 25 people on board were eventually recovered from the beaches around Frederick Henry Bay. The remaining 4 bodies were never found."Inquest On Air Crash Victims" The Mercury – 29 June 1946, p. 4 (National Library of Australia) Retrieved 19 September 2011 One body was found on the beach at Sandford, about 5 miles from the site of the crash."Body Found On Beach" The Mercury – 25 March 1946, p. 7 (National Library of Australia) Retrieved 21 September 2011 The body of the supernumerary pilot was not identified until 19 days after the accident."S.A. Victim Of Air Crash Found" The Advertiser – 30 March 1946, p. 11 (National Library of Australia) Retrieved 22 September 2011
Two years after the accident, a human thigh-bone was found on Seven-Mile Beach. Police believed the bone came from one of the bodies never recovered."Human Bone Found On Beach" The Mercury – 19 March 1948, p. 4 (National Library of Australia) Retrieved 26 September 2011"Bone Near Air Crash Scene" The Sydney Morning Herald – 19 March 1948, p. 4 (National Library of Australia) Retrieved 19 September 2011
Investigation The director-general of Civil Aviation promptly established a panel to investigate the accident. The panel was chaired by John Watkins, Superintendent of Airworthiness & Aeronautical Engineering."Pilot Of Crashed Aircraft Had Diabetes" The Argus. 4 May 1946, p. 3 (National Library of Australia) Retrieved 21 September 2011 After examining the wreckage recovered from the sea bed the panel was satisfied both engines were operating at high power at the time of impact and there was no pre-existing structural or mechanical defect that would explain the crash.
The panel arranged for the witnesses at Seven Mile Beach to observe a series of flights by a de Havilland Dragonfly taking off from Cambridge aerodrome, and to identify which flight best represented what they saw on the night of the crash. This exercise established that VH-AET reached a maximum height of about . The panel members were satisfied that, after take-off, VH-AET achieved a normal climb of about 325 feet per minute (1.6 m/s) and a gradient of about 1¾% before suddenly commencing a descent of about 17½%. Calculations showed that the aircraft's descent reached about 4,000 feet per minute (20 m/s) and its speed about before it struck the water.
The panel contemplated 25 possible causes of the accident."Pilot's Condition Probably Caused Air Crash" The Advocate – 16 May 1946, p. 5 (National Library of Australia) Retrieved 24 September 2011 In its interim report to the Director-General on 20 March 1946"Robot Pilot Engaged Before Crash" The Mercury – 15 May 1946, p. 12 (National Library of Australia) Retrieved 24 September 2011 the panel reduced these possible causes to 3:
Automatic pilot The control box for the automatic pilot was recovered from the wreckage. The control knob for its gyroscope was in the caged position and the CAGED warning flag was in view even though the control box carried a placard stating the gyro must be uncaged before takeoff. The automatic pilot's speed valve unit was also recovered; it showed that the three valves were open in positions indicating the unit was operating at the time of the crash. The investigation panel proposed that the automatic pilot might have been engaged at a height of about causing the aircraft to descend swiftly into the sea. Engagement could have occurred inadvertently when one of the pilots intended to select fuel cross-feed ON.Aussieairliners Retrieved 14 September 2011Aviation Safety Network Retrieved 14 September 2011 The operating levers for fuel cross-feed and automatic pilot were the same shape, the same height above the cockpit floor, and about apart on the cockpit control console.
No-one on the ground at Cambridge aerodrome saw the pilot who occupied the co-pilot seat prior to takeoff. The panel proposed that the captain may have asked the supernumerary pilot to occupy the co-pilot seat during the flight to Essendon Airport. The supernumerary pilot was on his third flight with the company and had no prior experience flying the C-47 or DC-3. The panel considered that if the supernumerary pilot had occupied the co-pilot seat, and if the captain had called for fuel cross-feed to be turned ON to deal with a fuel pressure problem in one engine, it was possible the supernumerary pilot's lack of familiarity with the DC-3 cockpit caused him to inadvertently engage the automatic pilot.
The panel used a DC-3 aircraft with a cockpit identical to that of VH-AET to carry out four flight tests with the gyroscope caged. When the automatic pilot was engaged the control wheel moved forward so strongly it was torn from the pilot's hands, and regaining control required use of both hands and significant force. Initial tests showed that when the pilot was unprepared, up to could be lost before he identified the problem and disengaged the automatic pilot. On the fourth test the pilot restricted the height loss to . The panel considered the most likely explanation of the accident was inadvertent engagement of the automatic pilot with the gyroscope caged.
Others Bird strike – A fortnight after the accident the mutilated body of a large bird was found on Seven-Mile Beach. It was considered the bird, which had a wingspan of about , may have struck the aircraft cockpit, distracting or incapacitating the pilots."Bird Possible Cause Of Air Crash" The Mercury – 1 May 1946, p. 1 (National Library of Australia) Retrieved 16 September 2011"Bird Might Have Collided With Cockpit Of Plane" The Mercury – 2 May 1946, p. 10 (National Library of Australia) Retrieved 16 September 2011 Alternatively, the bird could have struck the aircraft's pitot tube, damaging it and causing inaccuracy in the airspeed indicator.