16/09/2021

Valuable inspections

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A cylinder block stood the foundry in at just tens of £s, we looked at many more expensive items. For example, I was once asked to take my kit into the Natural History Museum. One of its scientists had established that a turtle could be ‘aged’ by examining the inside of its brain cavity. He passed me a skull, I shoved one of our rigid borescopes with video camera attached through an eye socket to display the skull’s insides onto a screen. Cameras were quite bulky back then and attached to the end of the scope the whole was quite unwieldy.

Prehistoric turtle skull

I asked about the origin of the skull and was told it was 110 million years old. It had been found as a fossil deep within stone that they had etched away with acid to reveal the skull. I carefully withdrew my scope and passed it to them, though they did not seem at all concerned about the possibility of damaging this precious object.

We also hired out our knowledge and equipment. On one occasion I was called out to Gatwick at 4am. A Lockheed L-1011 TriStar of Pakistan Airlines had lost its wheels on take-off, the problem was diagnosed as an issue in its truck-beam assembly, part of the landing gear. The CAA had ordered that all Tristars needed inspection within the next ten days, to look at an internal weld for signs of cracking. I arrived with a medical arthroscope, more often used for keyhole surgery on knees and other joints. It was just 1.7mm in diameter and this one had a sheath over it with a 90-degree lens at its end to provide a side view.

My major concern during the inspection was that the plane had recently landed and the fuel in its wings was cold from being at altitude. Sheets of ice had formed on the underside of the wing and were now falling in big slabs all around us.

We got the view and sure enough there was indeed a crack. The engineer, unfamiliar with my device, asked me what size it was. I scanned their drawings and knowing the magnification of the device came up with a calculation suggesting it was 8-to-10 thou. He promptly asked me to sign off against this, which I just as promptly refused because the aircraft would take off shortly with hundreds of passengers aboard, there was no way it was going to do so on my ‘back-of-a-fag-packet’ calculation and signature.

Rolls-Royce RB211 engine internals

On another occasion we were called to Rolls Royce Derby to see if we could provide a view of the first-stage turbine of an RB211 engine. By this time engines were being developed with ports built-in to allow views of key areas with a set of rigid scopes. There was one RR employee who during development phases would insert wooden cones representing the required view from where the port was to be located. But a late modification to this engine had moved one port. It was only slightly, but this meant it did not provide a view of the end of the leading edge of the first-stage turbine, and their first problem hit right there.

The last row of cooling holes in that blade were developing a crack that was not visible with rigid scopes through the port. They could see the trailing edge but by the time the crack had broken through, it was dangerous. RR was faced with issuing an instruction for more frequent inspections of that trailing edge, and this would be economically damaging.

We were asked to see if we could provide the needed view on a brand-new engine ready for shipping from Derby. I put a flexible scope in through the port but found that we needed the scope to enter the rotor space to get the clarity of view required. The production guy had a helper called Fred standing by and he called out ‘Fred, in a moment we will need to turn the inching drive’. Fred was a tad hasty and engaged the drive which flicked the rotor. My scope was suddenly delivering no image because the rotor had neatly chopped off the tip, severing the fibre-bundle. Worse, when I withdrew the scope it was evident its tip had been left somewhere inside this expensive new engine ready for despatch. These stainless-steel clad Olympus fibrescopes cost around £6,000 each. I used a medical scope to find and remove the tip and to look for any damage to the engine, thankfully there wasn’t, but it was clear we could not expect a maintenance team in the field to run a similar risk.

After many trips from Southend to Derby our bench team, mostly ex-watchmakers, came up with a guide tube that was inserted into the port and sat the scope safely outside of the rotor path. It had a timing lug that located into a sheath attached to the scope to give it the right orientation. A spring then allowed the user to push the scope forward into the rotor path once assured that everything was static. Letting go promptly sprung the scope back to the safety of the guide tube. Sadly, we could only bill them tens of £s for each device, sad because we had saved them many millions, and probably saved the future of the engine.

I spent a good deal of time visiting RAF stations, in particular their centre for NDT at RAF Swanton Morley. At this base was its Central Servicing Development Establishment (CSDE) and the Maintenance Analysis and Computing Establishment (MACE). Other regular visits were to the Army Air Corps at Middle Wallop and the Fleet Air Arm. I was checked into these places, had signed the Official Secrets Act, yet was rather surprised by the amount of unsupervised access I had to these front-line aircraft. I could just wander around in the hangars and on the aprons with no-one ever challenging my right to be there.

Of course, turbine generators were used as electrical power plants on North Sea oil rigs and in remote and developing areas and so the techniques we developed for aero engines had further applications. We also provided inspections of gun barrels, the fuses of shells and the interiors of missiles – it was pretty-much endless.

We inspected nuclear power stations and submarines. We found that the radiation quickly destroyed the fibre bundles so that scope life-expectancy was short. As was ours, because pretty quickly the whole team had exceeded the permitted exposure levels which meant we were not allowed to enter these facilities again.

ASIDE: Your exposure limit back then was defined by your age, minus 18, times a factor. But if you were born and brought up in Aberdeen, ‘Granite City’, you had a natural dosage that was twice the permitted level. We saw our ban from nuclear facilities as a badge of honour, hoped we might shine at night, something like the children featured in Scott’s Porage Oats adverts – though not really a joking matter.

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