Viscount 700 series similar to VH-TVC |
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| Accident summary | |
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| Date | 30 November 1961 |
| Type | Structural failure of wing in thunderstorm |
| Site | Botany Bay, Australia |
| Passengers | 11 |
| Crew | 4 |
| Fatalities | All (15) |
| Survivors | 0 |
| Aircraft type | Vickers Viscount Type 720 |
| Tail number | VH-TVC |
| Flight origin | Sydney, New South Wales, Australia |
| Destination | Canberra |
On 30 November 1961 a Vickers Viscount aircraft departed from Sydney, Australia late in the afternoon for a flight of 128 nautical miles (236 km) to Canberra. There were thunderstorms to the north and south of the airport. From about 9 minutes after takeoff the crew of Ansett-ANA Flight 325 did not respond to radio calls. The Flight did not arrive at its destination and authorities received no report of a crash. Throughout the night no-one knew the fate of the aircraft or its occupants.
The next day wreckage and a fuel slick were found on the surface of Botany Bay. The aircraft had been drawn into a thunderstorm and subjected to extreme turbulence. It had broken up and crashed into Botany Bay, less than 3 miles from where it took off. All fifteen occupants died.[1][2][3]
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Ansett-ANA Flight 325, a Vickers Viscount registered VH-TVC, took off from Sydney airport on runway 07 at 7:17 pm local time for a scheduled passenger flight to Canberra. On board were two pilots, two air hostesses and eleven passengers.[1][3][4]
Around the time of takeoff there was a severe thunderstorm with very heavy rain to the south of the airport and another to the north. There was cloud about 800 feet (244 m) above Sydney airport but no thunderstorm activity. Flight 325 was observed to enter cloud shortly after take off.[5] Five other aircraft took off while this meteorological situation existed.[1]
Flight 325 was directed to take-off and continue heading east towards the ocean until reaching an altitude of 3,000 feet (915 m), turn around and fly west to a radio navigation aid 6½ miles (10.5 km) west of the airport and then turn south-west for Canberra. The crew were to ensure they passed over the airport no lower than 5,000 feet (1 525 m).[1]
Five minutes after takeoff the crew advised they had reached 6,000 feet (1 830 m). About 3½ minutes later, Sydney air traffic control called Flight 325 with a routine request for information but received no reply. No further radio communication was received from Flight 325 so when it did not arrive at Canberra airport authorities knew it had suffered an accident. An air search of the route to Canberra was planned to commence at dawn.[1]
Approximately 9 minutes after takeoff the right wingtip[Note 1] had been torn away and the aircraft had crashed into Botany Bay.[3] The rain, thunder and lightning associated with the thunderstorm over Botany Bay had been so intense that no-one saw the aircraft or observed anything crash into the water. Accident Investigator Frank Yeend wrote "The weather was so bad that this aircraft crashed in the middle of a major city without anybody having seen it or heard anything that would give cause to alarm."[1]
| External images | |
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| HMAS Kimbla recovers wreckage from Botany Bay | |
| Navy clearance divers prepare to search for the right tailplane in waters to the north of Kurnell | |
Soon after sunrise the next morning searchers on Botany Bay found some of the upholstery from one of the pilots' seats and other floating wreckage. Searchers on the beach in the north-east of Botany Bay, near Bunnerong Power Station, found some cabin furnishings and body parts. The right wingtip was found protruding above the surface of shallow water near Kurnell.[Note 2][1][6][7] Later in the day Police and Navy divers investigated a large fuel slick in the centre of Botany Bay and discovered the scattered wreckage of VH-TVC in 25 feet (8 m) of water. The aircraft had crashed 2.8 statute miles (4.5 km) south-east of Sydney airport.[Note 3]
The Royal Australian Navy sent a team of clearance divers and HMAS Kimbla, a boom defence vessel, to bring the main wreckage of VH-TVC to the surface. After a week Kimbla was replaced by HMAS Walrus, a smaller workboat from which the Navy divers worked for many weeks, locating and recovering many smaller pieces of wreckage.[1][7]
The right tailplane was missing from the main wreckage. Navy divers eventually found the missing parts of the tailplane close to where the right wingtip was found, indicating the right tailplane was torn from the aircraft prior to its impact with the water.[7][9]
Numerous small items, including many from the number 4 engine nacelle, were found on Kurnell peninsular, south of the right wingtip. The wreckage trail was aligned approximately north-south with the main wreckage at the north in Botany Bay; and the smaller, lighter items at the south on Kurnell peninsular.[9]
The aircraft was not equipped with a flight data recorder or cockpit voice recorder so it was important that as much as possible of the wreckage should be recovered and examined.[1][11] The recovery effort continued for 3 months.[12]
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| Wreckage of VH-TVC laid out in a hangar. | |
As pieces of wreckage from VH-TVC were progressively recovered from Botany Bay they were laid out in a hangar at Sydney airport to allow investigators to search for the cause of the accident. The right tailplane and right wingtip had received almost no damage on impact with the water but the main wreckage in Botany Bay showed extensive disintegration, suggesting a very high speed of impact.[Note 4][10] No evidence was found of any fault or mechanical failure that might have existed prior to the accident.[1][7]
It soon became clear that the spar in the right wing had broken and the wingtip had been torn away by the airstream. The lower boom (or lower flange) in the wing spar had failed in upward bending at station 323 due to extreme overload. The wing had been overloaded while the aircraft was flying at very high speed, probably in excess of the maximum safe speed of 260 knots indicated airspeed.[1][3]
Engineers assisting the accident investigation calculated that for the wing spar to fail in the way it did in VH-TVC would require the aircraft to be flying faster than its maximum speed of 260 knots and, while being subjected to a severe recovery manoeuvre by the crew, to encounter a very strong gust, possibly as much as 100 ft.s-1 (30 m.s-1). At the time of the accident investigation, gusts up to 72 ft.s-1 (22 m.s-1) had been measured inside thunderstorms by suitably equipped research aircraft.[1]
All the wreckage lay in a trail aligned north-south. By making assumptions about the likely terminal velocities of key pieces of wreckage, accident investigators were able to determine the approximate location, height and speed of the aircraft at the time it broke up. They believed the right wingtip was torn away when the aircraft was south of its intended flight path, heading in a northerly direction, and at a height between 3,500 ft (1 067 m) and 5,500 feet (1 676 m).[14] They believed this occurred at a time when the aircraft should have been at about 9,000 feet (2 743 m), heading west and passing over a radio navigation aid nine miles away. It was necessary for the investigation to find a rational explanation as to why the aircraft was so far from where it should have been.[1]
Accident investigators studied a scientific report titled The Thunderstorm published in the USA in 1949. This report proposed that where two thunderstorms were separated, edge to edge, by less than 6 miles (9.7 km) there was a likelihood of severe turbulence in the clear air between the two. The accident investigators believed it was likely that Flight 325, while flying west between two mature thunderstorms, encountered strong turbulence that caused the crew to lose control and the aircraft to lose a significant amount of height and enter the thunderstorm to the south of the airport. While flying north, possibly in an attempt to escape the thunderstorm, the crew encountered continuing strong turbulence that caused control to be lost again. The aircraft accelerated to its maximum safe speed or faster and while the crew were struggling to regain control the aircraft was suddenly subjected to extreme turbulence that caused the right wing spar to fail.[1]
A Board of Accident Inquiry was appointed in 1962 to investigate all aspects of the accident to Flight 325.[1] Chairman of the Board was Mr Justice Spicer of the Commonwealth Industrial Court.[15] The Board first convened on 12 June 1962, sat for 24 days and closed on 27 July 1962.[1]
Investigation of the accident concluded:
The cause of the accident was the failure in flight of the starboard outer wing in upward bending due to tensile overloading of the lower spar boom at station 323, probably induced by a combination of manoeuvre and gust loading when the speed of the aircraft was in excess of 260 knots. The circumstances and available evidence carry a strong implication that the in-flight structural failure was preceded by a loss of control with a consequential increase in speed to at least 260 knots. The most probable explanation for the loss of control is that the aircraft entered an area of unexpected turbulence of such severity as to deprive the pilots of full recovery.[3]
The Inquiry gave a strong impetus for greater co-operation between the meteorological service and air traffic control; and for airline aircraft in Australia to be equipped with weather radar to give pilots of these aircraft the ability to avoid hazardous weather.[1][16] All Australian airliners were required to be equipped with weather radar by 1 June 1963.[17]
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| Photograph of VH-TVC | |
| Two photographs of VH-TVC in flight | |
The aircraft was Vickers Viscount 720, serial number 46. It was registered VH-TVC and first flew on 17 November 1954. It was delivered to Trans Australia Airlines on 8 December 1954 and named John Oxley in honour of an early Australian explorer and surveyor.[2][4][18]
VH-TVC was leased to Ansett-ANA on 7 March 1960 and operated with the passenger cabin configured for 48 passengers.[2][4][16]
The aircraft made 12,010 flights and flew for 16,946 hours.[2][4]
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