Boy Entrant; The Recollections of a Royal Air Force Brat (50 page)

A feeling of calm confidence had descended on me by this time and in a way, I was enjoying the experience. We moved along the row of consoles to where another type of voltage regulator squatted on the flat workbench. Here, the vertical paxoline board behind the bench wasn’t equipped as a console furnished with aircraft electrical components. Instead, it was configured as a tool-board of a type known as a shadow-board. Silhouettes of various common hand tools had been painted on the board to visually indicate which tool belonged in that space. The tools were held on the shadow-board by spring clips on or around the “shadow.” All of the tools were in place as we approached the bench, so the shadows weren’t plainly evident. We stopped in front of the voltage regulator and the Chief Technician looked down at it. I followed his example.

“I want you to do a mechanical setting on this,” he said, placing a hand on top of the regulator for emphasis, as he had done before.

The task was an easy one. The basic aircraft voltage regulator of that era was an electro-magnetic device that compressed or relaxed a “pile” of carbon washers in order to increase or decrease the current flowing to the generator’s magnetic field. The mechanical setting was a coarse initial adjustment, from which finer adjustments could be made to achieve the correct output voltage from the regulator when power was applied to the unit. We had been taught the procedure, which involved screwing the magnetic core all the way into the regulator until it bottomed and then screwing it out until two threads showed. Then, at the other end of the regulator, screwing the pile compression screw in until it gently made contact with the pile and then unscrewing it three-quarters of a turn and locking it. That was the extent of the mechanical setting. But simple though it seemed, there was a need to be wary because this type of question concealed a hidden trap that our instructors had frequently warned us about—although we had been taught the procedure, we weren’t supposed to perform it from memory. Instead, we were required to refer to the appropriate servicing schedule and follow a step-by-step set of instructions whilst performing the task. If I didn’t ask for the servicing schedule, I would lose marks.

“Can I please have the servicing schedule, Chief?” I asked.

Without a word, the Chief Tech immediately opened a drawer in the bench and produced a sturdy cardboard binder containing the servicing schedule, which he handed to me. Then he made a notation on his clipboard. Turning to the first page of the servicing schedule, which I had laid on the bench beside me, I proceeded to make the mechanical setting, using the special non-magnetic screwdriver required by the servicing schedule. It’s fair to say that I would probably have forgotten about the special screwdriver if I had failed to read the servicing schedule and that would have been two marks against me for the price of one.

We moved on to other things. Sometimes, I was asked to

trace out complex circuits on wiring diagrams and explain how the circuits operated. At other times, I was instructed to perform other servicing tasks and as with the voltage regulator, there was always a need to be conscious of using the correct procedures and observing appropriate safety precautions.

For one such task, the examiner set me to perform a battery change on the Hunter aircraft that stood in the centre of the workshop. The job itself was easy, needing only a little exertion to lift the heavy batteries. But I was also being examined on whether or not I used the servicing schedule and observed the safety precautions that it included, with regard to working with batteries. Handling them was one thing, because of the corrosive acid they contained, but there was also a need to observe certain precautions when connecting and disconnecting them from the aircraft’s electrical system. The negative battery terminal is always connected to the metal airframe, just as the same terminal of a car battery is always connected to the car body. The main reason for this is to save weight and expense by using the metal of the airframe as the return conductor to carry the current back to the battery for all circuits. When disconnecting battery cables, the negative side is disconnected first, to electrically isolate the battery from the airframe. This makes the creation of a hot spark due to an accidental short-circuit much less likely, which could otherwise easily happen if something metallic—perhaps a spanner—accidentally touched against some part of the aircraft frame while it was being used on the positive battery terminal. Sparks of any kind are something to be avoided around aircraft, where easily ignited aviation fuel is ever-present.

I disconnected the negative cable first, then the positive cable, before loosening off the bolts that clamped the two heavy lead-acid batteries in place. At this point, the examiner stepped forward and told me to assume that I had already removed the old batteries from the battery bay and had replaced them with new batteries. Now he wanted me to finish the installation. I then performed the procedure in reverse, first clamping the batteries in place and wire-locking the wing nuts that bolted them securely to the battery trays. Then I connected them up to the aircraft electrical system, reading the servicing schedule as I went along and making sure that reconnecting the negative cable was the very last item of the procedure.

I was now supposed to go into the cockpit and make sure that the instruments powered up when the battery isolation switch was operated to the “on” position. This action required that another very important safety precaution was observed. I climbed the ladder leading up to the cockpit. The Perspex canopy had already been slid all the way back on its rails, allowing free access into the cramped one-man space within. It only required a foot to be planted on the seat cushion down inside the well of the cockpit, followed by the other foot, before sliding down onto the seat while holding on to the top of the windscreen frame for support. Oh so easy! But there was one important thing to check first. Was the seat safe? Were the safety pins in the right places, making accidental operation of the ejection seat impossible? So, whilst still standing on the ladder and with one hand on the outside of the canopy, I peered through the clear plastic and saw that the large red metal disc attached to the pin was threaded through the triggering component of the ejection-gun firing mechanism, at the very top of the seat, to prevent accidental operation. So far, so good! Now, before stepping in, I needed to look down along the side of the seat to make sure the drogue gun pin was in place and then check for a safety pin in the alternative firing handle down on the front edge of the seat pan. Yes, they were both in place. I turned to Chief Tech Grim-Face, knowing full well that he was watching me like a hawk. “I’ve checked the seat Chief and it’s safe.” He nodded in understanding as I swung a leg over the lip of the cockpit and proceeded to enter. Then he came up the ladder after me, looking into the cockpit as I flicked the toggle of the battery isolation switch upwards and was rewarded by hearing a satisfying clunk coming from somewhere underneath the cockpit as the battery circuit breaker closed. Immediately, the aircraft’s electrical circuits energized. Gauges suddenly sprang to life, gyros started to whir as they spun up to speed, the “generator failure warning light” glowed red and all three “undercarriage locked down” lights glowed green. The artificial horizon chattered erratically for a few moments before settling down and the G4B compass card whirled crazily until I reached out to press a small button that brought it to an immediate stop.

We walked together to where the 700 lay on a bench near the Hunter. I searched for the correct page and then made the appropriate notation in the log.

The Chief Tech watched as I signed and dated the entry and then beckoned that I should follow him as he made his way to another console.

“I want you to perform a functional check on this circuit,” he announced, indicating a console that was wired up as an engine starting system. Everything was there except the engine and the electric motor that turned it during the initial phases of a jet engine start-up.

The starting system was designed to rotate the engine slowly at first and then cause it to speed up in two separate stages, in much the same way that a car is taken from standstill to normal road speed through successive gear changes. But the speed changes in this case weren’t achieved by changing gears. Instead, the electric current to the starter motor was initially kept low by inserting a very large resistance in the circuit. Then, when cued by a timing device, some of the resistance was automatically removed, causing the motor to turn a little faster. Finally, all of the resistance was removed and the motor was free to run up to its full speed. When the fuel in the engine ignited and made it turn faster than the electric motor, the starter system shut down.

Of course, all of this involved the participation of several electrical devices to make it happen and most of them were wired together, in faithful reproduction of the real thing, on the console that now confronted me. Other than the absence of a real engine and starter motor, the only other difference was a group of small, coloured indicator lights used to indicate the various stages of resistance as they were switched in and out of the starter motor circuit.

I asked for the servicing schedule and started reading it. All I needed to do was turn on the supply voltage to the console and then press the engine start button. The circuit should step through its three stages and then stop. But this was an exam and things weren’t going to be that easy!

The first indicator light glowed, showing that the resistance had been inserted into the motor circuit and, in real life, the motor and engine would be starting their initial rotation. I could also hear the whir from the clockwork timing mechanism as it was being electrically wound up, but when several seconds had elapsed and the second indicator light remained dark. Uh, oh, I thought, looks like we’ve got a snag! The servicing schedule wasn’t going to help here; this came down to tradecraft and the ability to think and work logically in order to track down the cause of the problem and then fix it.

First, I needed to check the obvious, although I knew in my heart of hearts that the cause of this fault was going to be anything but obvious. The second light hadn’t come on, so the most obvious and the simplest course of action was to check for a failed bulb. I didn’t know what Grim Face’s expectation might be. Maybe I was supposed to deduce that it wasn’t a simple bulb failure because of other less evident symptoms, so there may have been marks against me instead of marks in favour, but I had chosen a certain course of action and was determined to stick with it. I unscrewed the indicator light’s lens cap and removed the small bulb. The tiny filament looked intact when I held it up to the light but I flicked a finger gently against the glass envelope anyway, just to check for the telltale vibration of a broken end. It still looked okay, but that didn’t mean there wasn’t a fault.

“Can I have an Avo please, Chief,” I asked, referring to an Avometer, the brand name of a multi-meter used throughout the Service—the first three letters of its name was an acronym for Amps, Volts and Ohms. My examiner bent down and reached into a cupboard underneath the bench, withdrew an Avo and handed it to me. The way in which I handled this piece of test equipment would also be scored as marks for or against, so I proceeded carefully. The first thing I did was to lay it flat on the bench and check that it was zeroed, meaning that the pointer rested exactly on the zero mark when no measurements were being made. There was a ribbon of mirror that stretched across the face of the instrument parallel to the scale. To make an accurate reading, it was necessary to view the needle-thin pointer in such a way that it completely blocked its own reflection in the mirror. This ensured that the measurement was being viewed from directly above the pointer and not from an angle that would produce a false reading. I now looked down at the scale from directly over the pointer and immediately saw that it was several graduations off the zero mark. Peering down on the meter scale and with one eye closed to view the pointer accurately against the mirror, I carefully adjusted a small knob that mechanically moved the pointer until it hovered directly above zero. Having done that, I then rotated one of the two selector switches on the face of the Avo to read Ohms, a measurement of electrical resistance. This applied a small internal battery voltage to the two test leads connected to the meter, which could be used to test a circuit’s continuity. Before testing the bulb, I briefly touched one of the metal probes at the end of a test lead against the probe on the other lead and checked that the pointer on the Avo swung all the way across the scale, proving that the meter was working in this mode. Out of the corner of my eye, I saw Grim Face making a note on his clipboard.

Satisfied that the meter was operational, I touched the probes to the contacts of the bulb and wasn’t surprised when the pointer swung most of the way across the scale, confirming that the bulb was indeed “serviceable”, in RAF jargon. That confirmed what I really knew all along—that there was a more serious problem with the circuit.

There was a circuit diagram pasted to the front of the console and it was to this that I now turned for help in finding the problem. Referring to the diagram while probing around on various terminals, I discovered that there was one particular terminal on a relay that was “dead” when a careful study of the diagram indicated that it should be “live”. Aha, I thought, this looks promising. Picking up a screwdriver, I started unscrewing the small terminal stud to free the wire that was connected to it and immediately saw the Chief write something on his clipboard. Damn! I suddenly realized that the circuit was still live. Realizing that I should have turned the power off first, I mentally pictured marks being deducted for poor tradecraft and failure to observe proper safety precautions. Feeling a little rattled, I immediately reached over and flicked the console power switch to “off” before continuing to unscrew the terminal. Then, when it was free, I pulled the wire out of the slot and noticed that a small piece of insulating tape had been wrapped around the end to simulate the fault. My spirits rose as I pointed this out to the Chief. He simply nodded and made another notation; a good one this time, I hoped. After having peeled the insulating tape off the wire and reconnecting it to the terminal, I powered the circuit up once again and then pressed the start button. This time everything worked perfectly. The time delay whirred, relays clicked and the three different coloured lights glowed in the correct sequence as the circuit performed its function.