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Radio Development on the VC10


Radio Development on the VC10

Chris Mitchell worked for BOAC/BA Engineering for 30 years, and one of his tasks has been the function of Radio Development Engineer for the VC10 fleet. In the account below he writes about some of the challenges of his job.

"The start of my 30 year career with BOAC/British Airways was as the Radio Development Engineer for VC10. So when I came across the VC10 website all sorts of memories came back to me of the aircraft during the early 1970s and perhaps some of these may be of interest.

When I started at BOAC, the VC10 carried a third Pilot/Navigator complete with sextant and star charts etc. This was to back up the Long Radio Navigation aids namely Doppler Radar and Loran. One of my jobs was to investigate improvements in these systems as well as alternatives.

Doppler

The Doppler system was never very reliable and the computer consisted of a ball resolver, which for the uninitiated is a steel ball rotated by a motor which then drives two wheels and gear trains for track and cross track distance. The aerial generated four beams and was gyro stabilised to horizontal. It steered left and right to align with the track of the aircraft by equalising the Doppler shifts from the left and right hand beams. On reflection it is surprising that it ever worked at all.


G-ASGN seen with the two other airliners at 'Dawson's Field' during the hijacking

One aircraft had a stubborn problem in that there was a constant error of about 3 degrees, which could never be found on the limited ground tests. The Flight Manager got really upset after a few weeks of this and said that if the fault were still there after the Major Check he would ground the aircraft and only agree to it going back into service after a test flight. This was unheard of for a Radio snag so my job was on the line. We changed all the black boxes and the antenna, checked all the wiring and even re-aligned the aerial mounting plate. This later check was fun as it involved jacking the aircraft and suspending four plumb lines, two on the aerial and two on the airframe (with their bobs in little pots of oil) and squinting through a surveying device to line them all up. I donít think that this had ever been done before and it was certainly not done again. We found nothing wrong and the aircraft was dispatched down the route (I think to Sydney). The 'Voyage Reports' came back to me over the SITA network, the 3 degree error was still there, I could see my career with BOAC coming to an abrupt halt. Then on 'the News at Ten', three aircraft hijacked by the PLA and one was my VC10. A few days later I watched with a mixture of regret and relief the film of the VC10 (complete with Doppler snag) being blown up at Dawsonís field. A second benefit from this incident was that one of the few parts salvaged from the wreck was the Horizontal Stabiliser which was later cycled through the fleet and enabled the only really major fatigue modification on the aircraft to be completed without extending the Major Check downtime by 5 weeks per aircraft. Thus saving many hundreds of thousands of pounds!

(For more on the hijacking of G-ASGN see the 'Incidents and Accidents' and 'Hijackings' pages)

Loran

The Loran navigation system worked by having groups of widely spaced ground transmitters emitting pairs of pulses that were displayed on a CRT at the navigators station. The operator measured the time difference between their arrivals at the aircraft and plotted them along hyperbolic lines printed on special charts. This was later automated using digital computers but in those days it was all done manually. Various frequencies were used denoted as A B and C. A and B were for civil use and C used by the military. At one stage it was deemed necessary to evaluate C, which the equipment on the VC10 could not receive, so I had the job of modifying an aircraft by fitting a new receiver and antenna coupler. It was decided that Captain Brian Calvert (later a Concorde Flight Manager, and author of the book 'Flying Concorde') and I would do the first flight. I would check that the electronics worked and he would navigate. We chose a flight to Washington for the first trial and I got on early to install the back boxes and do the ground checks. Brian turned up at the very last minute, handed me a large envelope and said 'Sorry old boy, canít make the trip but here is the chart. I am sure you can do it all'. Well he may have been sure but I wasnít, but as we had the usual Navigator on board I wasnít too worried. So after introducing myself to the Captain I retired to the First Class for a couple of glasses of fizz. Once we were airborne I wandered up to the 'Office' and changed places with the navigator who disappeared for the rest of the trip into my nice first class seat. It all seemed ok however, the CRT had all the blips that it was meant to and the knobs did what they were meant to but then I opened the envelope and took out the chart. Well the cockpit on the VC10 was spacious by airline standards; but Brian had got the chart from the US Airforce. It was about 8 ft. x 5 ft. and the chart table was about 18 x 12 inches. For much of the flight the engineer and co-pilot were holding up the chart whilst I tried to trace spidery coloured lines to find our position. Luckily they all had good senses of humour, but it cost me a few drinks in the hotel bar that night.

Inertial Navigation

There was a big demarcation dispute when it was decided to fit the AC Delco inertial navigators on the VC10 fleet. It was full of Gyros and Accelerometers so the Instrument Engineers claimed it as their system, but it was a navigation system and full of transistors and this technology was familiar to the Radio Engineers. I was dropped into this half way through the design phase to manage the basic installation. Coupling this to the Autopilot remained with the Instrument guys. After installing a mile or so of wire and a couple of blown up boxes the first aircraft was ready. Both my Instrument Development Colleague and I would go on the first flight.

The rules negotiated by the management were that I would check out the functioning of the Navigation Computers on the flight deck; but the autopilot coupling would only be used after I had changed places with my colleague from the Instrument Section.

All this was carefully explained to the Captain who seemed to agree but he had that gleam in his eye when he saw the new toy in the cockpit. 'I am going on the course next week, how does it work?'. I explained about inputting starting-points and way-points etc. and gave him a spare instruction card.


Some of the avionics modules seen in the avionics compartment of A40-AB
Photo J. Hieminga

The route was East bound, via Beriut where we would pull the fuses and get off. I would monitor the computers along the airways, cross checking position heading and track against the VORs, then the autopilot coupling and CDI would be checked when we reached the over water segment. As we crossed the coast French ATC told us that our first VOR was unservicable. 'Can we program that as a way point' asked the pilot. I showed him how to do it. The Co-pilot set up the other two computers with this and then set in all the other way points. 'I suppose that this sets it up in the CDI' said the Captain twiddling the knob and that was the end of the carefully negotiated demarcation. The autopilot was coupled and we were 'hands off' till we got to the Med. Fortunately the flight crew agreed to delete the way-point and de-couple everything before my other half got on the fight deck, thus avoiding all sorts of disputes and the trip ended amicably. Beruit was lovely, then a few weeks later it was mostly rubble.

Autoland

A Cat 3 autoland system was designed by BAC for the VC10. This was a duplicate fully monitored system of Byzantine complexity. Remember this was before the digital age, it was all magnetic amplifiers and analogue computing. Effectively this meant that each function was done four times, and all had to work for the system to meet Cat 3 standards which of course they rarely did. The Radio systems bore most of the blame at the monthly project meetings and as I was the sole wireless man at the meetings surrounded by twenty instrument and autopilot experts from BOAC and BAC I didnít stand much of a chance. It was decided that the Radio Altimeters needed improving, not surprising really as they were made by STC to a design that must have been obsolete 20 years previously. The quote from STC for a modification package was horrendously expensive so I got lumbered to do it. I replaced all the coax cable with a special low loss version with a silver plated foil screen that was almost impossible to work with. We must have scrapped more cable than we used. We matched all the mixer diodes by individual selection and redesigned the monitor system completely. After about a yearís hard work the Radio Altimeters were working perfectly but the autoland system still did not perform. BAC then came up with a proposal for a package of modifications to all the other black boxes at a cost that made STCís proposal seem small fry. By this time I felt a little more confident as I had proved the point with the Radio Altimeters and as I had some spare time I sat down at my desk and calculated the probability that all of the boxes would remain working for the four weeks required on average to certify an aircraft to Cat3 standard after a defect. As I recall this worked out that on average a maximum of one aircraft in the fleet would be certified for half the time. I could not believe this result, so I rechecked the maths, re-read the books but could not get a better result. We had already spent millions on the system and were planning on spending several more. I could not believe that my sums were correct, but I wrote it up anyway and went thus armed to the next project meeting where the big mod package was planned to be agreed.

I dropped the bombshell at the start of the meeting by asking the BAC experts what their planned system reliability was. I got a few blank stares, they seemed to have experts there on everything except reliability, but it was agreed that they would show my workings to their specialists at Weybridge and find the errors. Much to my surprise, the mod program decision was deferred. The next meeting they announced that my numbers were wrong, I had omitted to take into account the system wiring reliability so the situation was actually slightly worse than I predicted. VC10 Autoland was promptly scrapped and work started on another mod program to save weight by removing all the surplus equipment. I never got any thanks for saving the corporation all those millions, possibly because I asked the Project Manager who had signed the contract; which had no guaranty that it would work or compensation if it didnít. 'Me' he replied and walked away.

Test Flights etc.

I went on a few test flights before non essential staff were banned. Not that I needed the ban, I decided to avoid test flights after BEA flew, I think a BAC 1-11, into a hill with several engineering staff on board. I decided that the drive to work down the A30 was enough danger for me. They were however quite an interesting experience. The stall tests were exciting, lots of noise, a shaking control wheel and then the nose dropping as the stick was shoved forwards by the stick pusher. The Yaw Damper tests were always the most sick inducing. They were traing a new test pilot on my first test flight. The 3 yaw dampers were tested by switching them all off, inducing a yaw with the rudder pedals and then switching one on and counting the dutch rolls till they were damped out. On this flight the qualified test pilot was in the right hand seat with the schedule and the trainee, a very experienced line captain in the left hand seat doing the flying. The yaw dampers were switched off and the pilot applied a little pressure to the right hand pedal. The nose swung a few degrees and the wing dropped a few degrees. 'this is doddle' I thought, I had been told that this was quite 'hairy'. The test pilot seemed to agree. 'not enough rudder input, you have to be positive' he then appeared to apply full rudder and the aircraft seemed to fall out of the sky, the horizon disappeared at a very funny angle and when I saw it go past the windscreen next it was completely reversed. I was glad this was before lunch!

The emergency oxygen supply was also tested, by depressurising the aircraft at altitude. All the pax were issued with portable oxygen bottles and one could watch the pink under the fingernails go white. There seemed to be no other symptoms. Nobody seemed to choke like they do in the movies.


The ELRAT (right) and the HYRAT (left)  seen in their lowered positions on G-ARTA, only the ELRAT was fitted to production aircraft
Photo Brooklands Museum Archives

The final test was the ELRAT (Emergency Lowered Ram Air Turbine). This was a small alternator with a fan on the front. It was mounted on a couple of parallel swinging arms and dropped into the air stream by pulling a lever on the rear of the pedestal. This was done at the very end of the test flight as the aircraft crossed the perimeter fence. This was because there was no retract mechanism and the generator was only rated to last an hour. so we did not want to wear it out. The lever was locked in position with soft iron wire to avoid accidental deployment. On one flight somebody used stainless steel locking wire by mistake. The pilot was not pleased at all as he had to pull very hard indeed. The reason for the short operational design life was that the only time it would ever be necessary to use it was in the case of a four engine failure. It seemed unlikely that it would take more than an hour before landing. Actually it was only used once in anger to my knowledge when a Super VC10, feeding all four from the fin tank, let the tank run dry. That time the ELRAT was dropped when the lights went out and it ran and ran for nearly all the flight.

There was also a HYRAT, a similar emergency hydraulic pump, on the original project drawings, but this was never fitted on BOAC aircraft. (But it was fitted to G-ARTA as the accompanying photo shows!)

Whilst I was working on the Radio Altimeters I wanted to check some voltages and waveforms during coupled approaches. The necessitated sitting in the equipment bay with meters and oscilloscope and so we decided to do this on a training detail, rather than a service flight, so as to get more landings and not disturb the punters. We set off to Bedford, which had a Cat 3 ground installation, with half a dozen 'Space cadets' aboard, and a very experienced training Pilot, I think a Captain Alabaster, in charge.

After half a dozen coupled approaches, I had completed all my measurements and stowed the gear away. 'Grab a cup of coffee and come and see what the boys have learned on the simulator' said the captain. I didnít know at the time, but this was the first time the pupils had actually flown an airliner. I got a cup of that awful brew that passed for coffee on BOAC and wandered back to the fight deck as they started the first approach for a touch and go.

'You are rather long, you need to get closer to the numbers' was the Captains first comment, then 'a bit earlier with the thrust reversers' then 'no shove the throttles right forward a bit quicker'. I was getting the impression that we were rather a long way down the runway so I ducked down to look forward as I was still stranding up. The little wooden shed on the centreline at the end of the runway which contained some radio monitoring gear seemed to be ominously close and the nose wheel was still bumping down the runway. 'Now rotate, be positive' said the captain as I was trying to sit down in the navigators seat and find the safety harness, which is not easy with a coffee cup in one hand. I glanced forward, the wooden shed now seemed to be the size of a large house and the main gear was still on the runway. I was still trying to fasten the safety harness when we lifted of the ground a climbed away. The training captain debriefed the trainee reinforcing his comments and sending him back to get the next trainee. He didnít seem to be bothered so I assumed that I had been worrying unnecessarily. The remaining attempts were uneventful and we returned to Heathrow.

The captain was a real gent of the old school and helped me carry my gear off the aircraft, as we strolled across the concrete to Tech Block A. I said that I had been a bit worried on the first approach but that he did not seem to be concerned. 'Well Chris' he said 'I shit myself, but you must not let the pupils know'.

Lighting Strikes

All aircraft get hit by lighting and the VC10 was no exception. There was always a dispute between those who thought that aircraft attracted lightening and those who believed that they just happen to get in the way. I had to monitor all the aircraft technical logs for repetitive defects and once I found an aircraft, which had a poor ADF performance. I came to the unpopular conclusion that it was a problem with the Aerial, which was installed on the top of the fuselage. Changing this required the aircraft to be docked in the hangar which was time consuming and expensive. The problem with this aircraft had started after it had reported a lightning strike. The 'post strike inspection' had been done down the line and no defects found, but when we got the aircraft into the 'wing hangar' a different story was immediately apparent. There was a series of holes, on the top of the fuselage, right through the skin at about 18 inch intervals, increasing in size from one eighth of an inch to an inch and a half over the first 3 strobes and then tailing off for another 5 or 6 holes. No pressurisation leaks however, because the insulation bags were pushed up against the hole in flight by the internal pressure. A simple aerial change extended into several days whilst they patched the holes.


Close up of the nose of A4O-AB showing the weather radar radome with static discharger at the front
Photo J. Hieminga

In the early days of operations, before I had joined BOAC, a VC10 had been struck on the Weather Radar Radome. This had blown the radome apart and the blunt front had made the Pitot Static information unusable and the aircraft had to use a military chase plane to provide airspeed data in order to land. To avoid this problem Boeing fitted thin metal foil strips to the outside of the radome, which would vaporise when strick by lightening and thus hopefully conduct the charge to the fuselage without blowing the radome off. BAC, never ones for lightweight solutions, installed several metal strips 'Inside' the radome. These were joined at the front to a metal boss at the nose. Fortunately to my knowledge we never had another radome strike as I suspect that the bars would have vaporised and blown the complete assembly off the aircraft.

The metal boss was fitted with a special 'Static Discharger' which was always found to be u/s every time it was checked. At £25 each, this was quite expensive so we replaced this with a piece of electrically conductive plastic. This probably did not discharge much static, but we had no noise problems and it never need to be changed."

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