Frank Yeend was an officer of the Air Safety Investigation Branch of the Department of Civil Aviation from 1953 until 1975. He was Head of the Branch during the last three years of this term. During these 22 years he was involved in many field investigations involving aircraft accidents, and in the Boards of Accident Inquiry subsequently established.

This is Frank's recollections of the investigation of the accident involving the loss of the Vickers Viscount VH-TVC.

On 30 November, 1961, which was the day after I had completed my report on the T.A.A. DC-4 accident on Bulwer Island, Brisbane, I was notified in the early evening that an Australian National Airways Vickers Viscount VH-TVC en route to Canberra had taken off at Sydney shortly after 7.00 p.m. and, subsequently, all communication had been lost. When there was a continuing lack of communication response and the aircraft did not arrive at Canberra, we knew we had an accident somewhere and the 'go team', under Alan Lum, was hastily assembled.

We left Melbourne in the Department's Fokker Friendship at about 1.30 a.m. and arrived in Sydney at 3.40 a.m. The airsearch of the planned route was being organised, to commence at first light, but there were no reports from anywhere of an aircraft down. The media was already speculating that the Prime Minister might have been on board, but this was quickly denied by the operator. Soon after daylight, search vessels on Botany Bay found floating wreckage and this quickly narrowed the focus of the whole search operation. Later in the day an oil slick led us to a site in the bay where the main wreckage was later identified by police and navy divers.

Of course, all 15 passengers on board were lost, including some well-known Canberra residents. The main wreckage was in 25 feet of water 3 miles south-east of the airport, but a further 3 miles away, in very shallow water, we found the starboard mainplane, which had obviously separated from the aircraft in flight. This was before the days of flight data and cockpit voice recorders and so we had to set about recovering as much of the wreckage as possible for a painstaking examination. We had great assistance again from the navy clearance divers and their heavy-lift vessel, H.M.A.S. Kimbla. As it was recovered, the wreckage items were removed to a large hangar on the airport for identification and layout in a conventional pattern.

Under Alan Lum's overall direction, I took charge of the Operations Group, while Jim Doubleday was in charge of the Engineering Group and Dr John Lane, the Medical Group. In the Operations Group I had the assistance of Jack Macalister, Russell Watts, Alan Woodward and Eric Moore of the Department, as well as Captains Green and Butterworth from Ansett- AN.A and Captains Goodall and Britten from the Australian Federation of Air Pilots.

In the first ten days, the Operations Group was heavily involved in interviewing the many witnesses, who either offered assistance or lived in positions where vital sightings might have occurred. The general comment from all these witnesses was that the weather was atrocious at the relevant time, with very heavy rain, as well as continuous lightning and thunder. 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. Despite a major effort in pursuing witness evidence, in the end it told us nothing about the aircraft that we could not deduce from other evidence.

The aircraft took off at 7.17 p.m. towards the east at Sydney airport, with an instruction to continue in that direction to a height of 3,000 feet, then to turn about and come back over the airport at a height not less than 5,000 feet. This procedure was to ensure safe separation from other aircraft approaching the airport from the west to land on the 07 duty runway. Almost 5 minutes after take-off the aircraft reported it had reached 6,000 feet and it was cleared to proceed to the Padstow locator, 6.5 miles west of the airport and thence to Canberra. Some 3 1/2 minutes later Sydney Tower asked for a set course time, but there was no reply.

The accident investigation continued for approximately 6 months for the core participants. There was an early decision by the Government to conduct another public Board of Accident Inquiry and so there was great pressure to get to some point of conclusion as to how and why the accident happened. The examination of the relevant operational documents revealed no significant errors or shortcomings in any of the involved persons. The investigation became a matter of waiting for the conclusions of the Engineering Group and then endeavouring to interpret them in the operational context.

In due course, it became clear that the starboard wing had broken off, probably at a height of about 4,500 feet above sea level when the aircraft was travelling at very high speed in a northerly direction above Botany Bay. This was at a time when it should have been at a height of about 9,000 feet at the Padstow locator - a point at least 9 nautical miles west of the deduced point of wing separation and at an altitude 4,500 feet higher. The task of the Operations Group was to reach some rational explanation of this extraordinary discrepancy, particularly in the absence of any emergency communications from the flight crew.

The wreckage examination produced absolutely no evidence of fault in the aircraft other than the failure of the lower wing spar boom on the starboard side under conditions of extreme overload. The Viscount series of aircraft were built by Vickers-Armstrong under the "safe-life" design principle. In other words, the aircraft was strong enough to resist any serious structural failure during the whole of its designated life. The competing and now widely adopted principle of "fail-safe" in aircraft design contemplates some failures, but there will always be redundancy or back-up in either design or maintenance procedures to avoid a catastrophic failure.

The engineers calculated that to fracture the spar boom in this aircraft under over-load would require it to be flying at or above its "never-exceed" speed of 260 knots, then to encounter a sharp edged gust of at least 100 feet per second, and at the same time, probably experience a severe manoeuvre load as the pilots endeavoured to maintain control. A gust in excess of 72 feet per second had never been recorded in many hundreds of thunderstorm penetrations by measurement equipped aircraft. Obviously control of the aircraft had been lost first of all to remove it so far from its intended flight path and altitude at such a dangerously high speed. The task of the Group was to consider how this could occur.

At the time of this accident an occluded cold front aligned north to south was passing through Sydney, moving from the west in a general east-south-east direction. Embedded in this front was a series of thunderstorms of varying size, with multiple cells in each and with tops up to at least 35,000 feet. Of particular significance to this accident was the proximity to the airport of two thunderstorms at the time VH- TVC took off. One thunderstorm was centered over the Cronulla area, with its northern edge reaching the centre of Botany Bay. Another storm was centered over the city area, with its southern edge reaching almost to the airport boundary. They were both very visible to the eye, with heavy rain falling from each.

The airport itself, however, was relatively clear of cloud and rain when VH-TVC taxied for departure. As part of my area of investigation, I made an in-depth study of a report published in America in 1949 called The Thunderstorm, which described a deliberate programme of many storm penetrations by aircraft equipped to measure their internal force. There was a great deal of useful information in this report, including the proposition that when mature thunderstorms were separated edge to edge by less than 6 miles, the likelihood of severe turbulence occurring in that intervening space was very high. The very cold outflow air at ground level would undercut the warmer ambient air, driving it upwards and, in time, creating new storm cells. This was precisely the situation in which VH-TVC took off and endeavoured to transit twice this apparently clear area between the storms.

There are many circumstances which might generate loss of control of an aircraft, ranging through crew incapacitation for any number of reasons, flight instrument failures, flight control defects, structural failures, engine failures and so the list goes on. We considered them all, looking for the slightest bit of evidence in the wreckage which might support any one of these possibilities. We were eventually driven to the belief that, in the climb out towards the Padstow locator, the aircraft had encountered extreme turbulence inducing a complete upset and possibly stall, from which the flight crew had great difficulty in recovering. If, for instance, the aircraft had been turned on its back under climb power, the acceleration in a dive would be very quick and very high speeds would be quickly attained. Recovery would almost certainly involve a reversal of direction, a rapid loss of height and very severe flight control loads to arrest the descent.

Such a loss of control could so easily have carried the aircraft into the worst of the storm over Botany Bay, where even greater turbulence might be encountered. This would accentuate the need to turn away towards the known clear area over the airport. This cannot be more than a theory, but the combination of high speed, extreme turbulence and desperate recovery actions could explain the overload failure ofthe wing.

The Board of Accident Inquiry convened in Sydney early on 12 June, 1962, under the chairmanship of Mr. Justice Spicer, assisted by Captain Colin Howard, Douglas Hudson of Qantas and Howard Wills from the Department of Supply. The counsel assisting was Ray Reynolds QC. John Starke QC appeared for the Department, George Lush for Australian National Airways, Gordon Samuels - later Governor of N.S.W. - for Vickers-Armstrong and Arthur Pearce for the Australian Federation of Air Pilots. There were others, but these were the main players at the bar table. The Board heard evidence or addresses on 24 separate days and concluded on 27 July.

In two sessions I spent a total of about 3 days in the witness box, explaining the detail of the report of the Operations Group, which I had written and answering questions or propositions arising therefrom. This was quite a demanding experience because of the intense concentration required and the scope, depth and accuracy of memory entailed. My reasoning and reconstruction of the evidence was not seriously challenged at any stage and, indeed, the final conclusions of the Board were a complete adoption of the thesis I had proposed. This was another accident where the conclusions as to the cause could not be better than a theoretical reconstruction of probable events, simply because there was no evidence to support any alternative.

The most notable results of this investigation included a strong impetus to the requirement for airline aircraft to be equipped with weather radar, which would enable the pilots to negotiate hazardous weather more safely. It also gave rise to an operating arrangement called JACMAS or Joint Air Traffic Control and Meteorological Air Service, which existed for a number of years thereafter. This arose from some rather unfair criticism of the airport Controller who cleared the aircraft in circumstances where encounters with severe turbulence might be expected. The Board, of course, had the benefit of hindsight and the ultimate decision to go or not to go rested with the pilot-in-command. It is significant that 5 other pilots operated safely through this storm situation and none of them expressed any reluctance to proceed.

There was also some Board criticism of Alan Lum and the Department for not providing them with transcripts of the relevant communication frequencies until late in the proceedings. This was also a mis-directed shot because it was an unnecessary tactic adopted by John Starke as part of the warfare between the Melbourne bar and the Sydney bar, to which Ray Reynolds belonged.

The accident, the investigation and the public inquiry all received a great deal of media exposure, principally because of where the accident occurred and the fact that by this time the Vickers Viscount had become the front-line aircraft for air travel in Australia. The investigation certainly improved my knowledge of the aircraft type, of thunderstorm meteorology, of aircraft design parameters and of the problems of witness evidence. It was also another valuable experience of multi-interest investigation, which served me well in my international negotiations at ICAO a few years later.