Setting Standards

The test standards and performance specifications for aircraft wiring established by the Federal Aviation Administration (FAA) are virtually nonexistent. One limited test of wire performance is called for - the so-called 60� flame test, in which a wire is held at that angle, exposed to a direct flame, and the insulation must self-extinguish after burning a short distance. The test does not assess toxicity, smokiness, durability, and such, nor is the wire under electrical power. The need for a more demanding and realistic standard was noted by the Transportation Safety Board (TSB) of Canada in its investigation into the Swissair Flight 111 tragedy (see ASW, April 7).

The GAMA/AIA letter to ATSRAC (mentioned above) suggests in its proposed advisory material: "In considering the acceptability of wire, reference should be made to industry standards that define acceptable test methods for aircraft wire, including arc tracking test methods."

Among the "industry standards" referenced is document EN3475. Upon further research, this document turns out to be UK Ministry of Defence Standard 61-12 of Nov. 25, 2002, for aircraft wires and cables (see http://www.dstan.mod.uk/data/61/012/33000400.pdf). The detailed wet and dry arc-tracking qualification tests laid down in this document reflect the bitter experience of the Royal Air Force with aromatic polyimide wiring (see http://www.iasa.com.au/RAFkapton.htm).

The term "industry standards" for wiring begs the question of regulatory standards applicable to commercial practice, which are nil.

One could compare the regulatory paucity to an Egg Marketing Board leaving it up to the chickens to fulfill the requirement for sufficient eggs of a certain grading of sizes (and with the chickens determining the specification and standard of finish, thickness, brittleness and durability of the shell, yellowness of the yolk and whiteness of the egg- white). When the day comes that a batch of sulphurous rotten eggs explodes, it will not be the fault of the chickens or of the Egg Marketing Board. The eggs were just too old and evidently never refrigerated properly.

As the TSB pointed out, a wire systems harmonization working group has been tasked to develop performance standards and tests.