Aging wiring and associated deterioration of the insulation increases the probability that ticking faults will occur in our aircraft. Aging Wire Laymen tend to think of aging only in terms of elapsed time. However, when it comes to aircraft structure and components, including wiring, the aging or degradation of these items is also a function of the operating environment and conditions that they are exposed to. The term 'aging' when used to refer to wiring primarily denotes the deterioration or failure of the insulation, as opposed to the conductor. Aircraft wiring aging rate is principally affected by the four factors discussed below.
Vibration is one of the factors affecting wire aging.
Vibration is not at a single, constant level throughout the aircraft. It varies greatly as a function of location in the aircraft, and as such it affects the wiring running through those areas differently. Mixing wires of different types in the same bundle has been shown to be detrimental to wire life, because the harder coating on one wire can cut through the other when the wire bundle is subject to vibration. Wheel wells, engine compartments, and areas near the air-conditioning packs all have different vibration cycles, and yet the current regulatory and industry approaches to wiring do not take those differences into account. As mentioned previously, moisture is another major contributor to wire aging.