SASless also had the joys of dealing with his Nemesis, the delightful, Gallic, much-loved, baby producing Count WithoutanO. No matter how old SAS may be now, he can't possibly be as old as the Kapton wiring still residing inside the rotting bowels of BDD despite a recent D check. I'm sure that they saved a lot of money, but maybe some of those who now have to fly it, both crew and passengers should consider the following:
Kapton - the aromatic polyimide wiring insulation around the wire strands - has no place, in passenger-carrying aircraft. The main reason is that, in an electrical short, the wiring insulation chars to a conductive carbon residue and ignites like a dynamite fuse, affecting the whole wiring bundle (and therefore many disassociated systems). The phenomenon is known as arc tracking. Because the outer carbon char (and not the internal wire-core conductor) is then carrying the current, the circuit breakers most probably will not trip. There is therefore nothing to halt this "flashover" because the power stays on the wire. The older the Kapton wiring gets, the more brittle and vulnerable the insulation becomes. The wiring clearly is not safe.
Even though the British CAA (Civil Aviation Authority) has forbidden the use of Kapton insulation in new aircraft designs, a loophole allows it to be used in current designs. Despite ample warning about its dangers, the Royal Air Force took delivery of Kapton-wired Harrier GR5s. Two crashed because of the wire before the RAF embarked on a program to modify the use of Kapton in all the vulnerable parts of their planes.
In the early eighties, a US naval captain discovered an obscure Soviet technical publication, 10 years old, which analysed Kapton (technically an aromatic polyimide). The publication noted that the insulation decomposed when in contact with concentrated alkali but, more chillingly, the insulation was hydrolitic - it absorbed water. (Just great in a warm, damp climate like that of Nigeria). The report also mentioned Kapton's tendency to arc.
The US Navy, already alarmed at a rash of wire failures and unexplained flash fires in its fighter planes commissioned detailed tests of Kapton. These were conducted by Bob Dunham, its top civilian expert on aircraft wiring. Dunham's tests revealed a terrible truth about the now widely installed insulation. Kapton's positive aspects were heavily outweighed by its uniquely negative qualities. Its strength was negated by the fact that it had "straight line memory". It always wanted to return to its original position when on a wire drum. This meant that unless it was properly and frequently imprisoned in clamps it had a tendency to "roam" and subsequently chafe. Its ultra-light weight (only three and a half human hairs thick) was a huge commercial advantage, saving precious weight on the plane. But when the insulation wore through and the naked wire touched metal, it arced at 6000 degrees, and before short circuiting it flashed like a tiny banger firework.
Dunham's experiments then discovered that when the short circuit tripped the circuit breaker (fuse box) in the plane, once the breaker was re-set and the power restored to the wire, a new flame ran along the Kapton insulation, turning it into a charred flame conductor. In this way, fire spread along the path of the plane's wires.
Dunham, who videoed the tests, was appalled. So was the US Navy. By 1987, it had mothballed many of its Kapton-wired planes and unceremoniously banned Kapton.
So, if you're flying that good old heap of Double Dung and you have a fire, sue the crap out of Bristow for allowing it to continue shaking its way through the sky with a product which has been proven unsafe and is banned in new aircraft by the CAA
