A short section from my dads book about his air accident investigation work at Farnborough, Hampshire, England.
This is regarding the Vickers Valiant disaster.
In 1956, one of the V-Bombers was being used at Farnborough in a variety of roles. It was instrumented and equipped for measuring such things as structural vibrations and deflections and other parameters of interest to aerodynamicists and structural engineers. One such experiment required the use of electrical energy, and conveniently this was drawn from one of the bomber’s domestic services at the navigator’s station.
It must be pointed out that this particular type of aeroplane was rather unique; its controls were fully electrically operated and not by some form of hydraulic power assistance as with other contemporary aeroplanes of such a large size.
As a type, this bomber has been flying quite successfully and had never experienced loss of control due to major electrical failure. As far as possible, the designer incorporated safeguards against all possible eventualities. The safeguards included not only the usual fuses – much like those used domestically in the home, only larger – but also circuit breakers. These are spring loaded switches which ‘pop out’ under excessive electrical loading, thereby protecting the associated circuit and equipment.
On Friday 11 May 1956, just after lunch, the bomber left Farnborough to carry out a flight, primarily for a scientist to conduct the experiment connected to the electrical outlet at the navigator’s station. The aeroplane had full fuel tanks and was likely to be airborne for several hours. On the way to the south coast, the scientist switched on the experiment. Almost immediately the appropriate circuit breaker ‘popped out’. Imprudently, the scientist reset it, and it again ‘popped out’. The scientist reported the situation to the pilot that his experiment could not be carried out, and because this was the main purpose of the flight, the pilot decided to abort the flight. However, before returning to Farnborough he had to use up a large quantity of fuel to bring the landing weight to an acceptable figure. He had taken off fully laden and was now returning very much earlier than originally intended.
The pilot set up a low level flight pattern over the sea off the south coast with conditions set for maximum fuel consumption. The flight continued quite satisfactorily for some considerable time. During this, the bomber was flying in and out of low cloud near to Shoreham and Brighton.
Now it seems that while this was being done, the scientist could not leave well alone, and in went the circuit breaker, not once by several times. Suddenly the pilot felt a stiffening of the controls and saw indications on the instrument panel of an electrical failure of major proportions. He immediately eased the bomber into a climb to make height for he now had a major emergency on his hands.
The bomber emerged from cloud at about 1,000 feet over Shoreham. Due to the electrical failure the flying controls were completely unresponsive. The pilot ordered everybody to eject.
They were now descending fast towards Shoreham railway station. At almost the last second, one ejector seat was seen to leave and its occupant made a short but safe descent, landing not more than fifty yards from where the bomber struck the railway embankment, near the station. All other crew members perished in the crash although the escape hatch was found away from the bomber. The aircraft disintegrated upon impact and debris was strewn for hundreds of yards across the playing fields of a nearby school. Mercifully, the fields were clear of pupils at the time.
Within an hour I was being flow down to Shoreham from Farnborough, and as it was only twenty minutes flying time, I was to make this trip several times in the next few days. Discussing the accident with the manufacturer’s design staff as we walked around the wreckage, some of the story of the flight began to emerge. A certain amount of information had already filtered through from Farnborough Control Tower and of course there was the surviving co-pilot. It was clear that there had been a major electrical failure and in company with the manufacturer’s chief electrical engineer, we paid special attention to the state of any electrical components that we could see.
The engineer appeared next morning having spent much of the night working on a hypothesis to account for much of what we knew. Could the wreckage evidence support his theory, or would it produce some other explanation?
We isolated as much of the electrical material as possible from the wreckage and this was sent to Farnborough. The remainder of the wreckage was to follow. There was an air of supreme urgency as other aeroplanes of the type could have been at risk. Our searching and examinations, along with the work of the electrical design staff at the manufacturer’s works, had shortened the list dramatically. It now transpired that if, as we suspected, the circuit breaker had been repeatedly reset, then the consequences must have included the ‘blowing’ of many fuses, but one in particular – the navigator’s station equipment circuit – would really prove the theory.
My priority task became the search for that one fuse to determine if it had ‘blown’ electrically. The fuse in question was about three quarters of an inch in diameter, and about one and a quarter inches long. It consisted of a heavy ceramic body, with metal end caps, attached by bolts to heavier items known as bus bars. There were many such fuses fitted in banks or rows in the bomber and although originally marked with paint for identification purposes they were broken and now devoid of such identify. They were also mixed with tons of twisted and burnt looms of wire and metal.
My fuse, either intact or in pieces was in the large mound of wreckage now at Farnborough. It was the Whit Monday holiday and I planned an assault on that mound. I had the help of skilled, semi-skilled and unskilled people. The approach was simple. I formed a pyramid of searchers with the unskilled at the mound. They were briefed to sort out all wreckage of a certain character. I made sure they would include more material than I wanted to ensure that the right stuff would come through for searching. Unwanted wreckage was discarded and required material passed back to a second row of helpers who had been briefed in more detail. They in turn passed back this selected material, and so the search continued. Each row of searchers was more qualified to select than the one before, and I was at the apex of the pyramid to make the final decision.
By patience, persistence and careful search and study, we discovered the first of the end caps after only two hours. It was still bolted to a piece of identifiable bus bar, although this itself had been badly damaged. An hour later the other end cap was found. Both caps contained pieces of ceramic body protruding but not mating to make up the body. We found other odd pieces of ceramic and one of these made the link between the end caps: I had my fuse.
I took the end caps to my microscope and there was the evidence that I sought. Traces of fuse wire had been electrically overloaded. The wire ends had formed into globules – a tell-tale sign of a fuse melted by electrical overheating and not by crash fire burning.
We now knew that the electrical supplies in the bomber had been disrupted by the repeated resetting of the circuit breaker – a senseless, illogical action which had led to tragedy and loss of life, including the life of the instigator of the situation. The repeated resetting of the circuit breaker was akin to tackling the symptom and not the cause of the experiment failure.
However, the accident prompted a long hard look at the electrical circuitry of all the large bombers and some shortcomings were brought to light. As I have said on other occasions, regretfully, in aviation someone must suffer, it seems, if aeroplanes are to be made safer.
This passage was extracted from the book “Air Crash” The Clues in the Wreckage.
ISBN 0-86379-094-1. Published in 1986. This book was written by Mr. Fred Jones ©.