Issue Number 6

February 2006

THE DREADED DEFECT

by Dave Sidgwick 681112 Engines

For ten years I flew as a Crew Chief on the VC10 aircraft. Not for me the flying suit (grow bag) and bone dome. By comparison this was a lounge suit job. I had done the pre-service project team and so a couple of us were deemed likely lads to do the crew chiefing task. Twenty-four weeks of training covering all trades were sandwiched in between trips. This multi-trade training served me well until I retired from the civilian airline industry recently.

Excellent though the training was I think it is fair to say that we all had the defect we dreaded. I certainly did. FLAP or SLAT ASSYMETRY! What a nightmare. Those who know me understand that I am probably the World's worst electrician. The day that I made the "break through discovery" that green was earth - they changed it.

There exists on the VC10 what is, for me, a hyper complex protection system preventing the flaps or slats deploying asymmetrically. Synchronised transmitters and receivers are employed, transmitters inboard and receivers outboard (or is it the other way round). When the flaps or slats move these two check each other's position. If the inners get out of whack with the outers the receivers and transmitters get out of phase and lock out. Thus the offending system stops, asymmetry is prevented and unrehearsed aerobatic manoeuvres are avoided. Add to this cocktail that the left and right systems talk to each other and the plot thickens. To make matters worse the whole nine yards works on milliamps and their brothers mill volts.

An "expert" like me can poke about with an AVOMETER with some success - sometimes. The theory is that if you make a mistake there is smoke - go to the source and that's where the defect is. But milliamps/volts - give me a break.

Prior to the situation I found myself in on this day one of our number had had this defect and had poked about with his mini-avometer. He had put a probe where he shouldn't and his mini-meter had turned into a one-kilowatt electric fire, albeit for a very short period. I resolved not to get into this mess if I could avoid it.

In the sixties the art of "potting" electrical components, that spend their entire lives outside the aircraft in inclement conditions, was not what it is today. In those far off days transmitters and receivers were merely double poly-bagged and tie wrapped. By removing panels I found the one, which looked dodgy i.e. wet. Right wing outboard. Cursing the day they decided to include a spare in the spares pack, (previously you could call for help and adjourn to the bar) I got out the wiring diagrams. Navigation is not my forte either - as Tod Slaughter who travels with me to the reunions will testify - thus I am not good on the London Underground and this drawing looked like an inky footed spider had gone berserk on an Underground map. So, forget the diagrams, at least for now.

Using masking tape and a biro for identification numbers I gingerly removed all the connections from the dampened item - about six as I recall. I still had not reset the failure so the problem was still in the system. Whilst I had been removing all the cables and so on I had warmed up one of the galley ovens. Taking care not to turn the quill drive I placed the offending item in the oven - now switched off and cooling slowly. Leaving it to its own devices I went off and did some more routine work - like kicking the tyres. It proves nothing kicking the tyres but they've done it over the years and it makes you feel good.

Gingerly I carried the offending item to its position and reconnected the cables I gave the whole thing a good dousing in WD40 (for the wife and kids this). I had taken great care not to turn the quill drive. My theory was that if the damp had caused the problem the inboard unit would still be out of whack with the outer and giving me an indication of asymmetry. Now the damp was removed, by heat and WD40, the system should realign itself if I selected RESET. I asked a passing American airman to put his ear to the unit whilst I went upstairs and RESET. He was to listen for any action but not to turn the quill drive. When I got back down he said that it had not turned but had "sorta kicked". I refitted the unit hoping that this kick was the problem going away. Back upstairs I operated the flaps and bingo the system was fine. Tidy up, fit the panels and head for the hotel. The crew were surprised the defect was cleared. I said that I had not replaced the unit but had fixed the defect.

That was the end of what had been the Dreaded Defect on this occasion. Time had been saved and the prospect of an ab-initio sparky getting things hopelessly wrong during the testing process with milli thingies and ampi watsits had been averted.

Sometimes you get a bit of luck.

Adaptable, ingenious and resourceful, the mark of the 81st!