Health management for avionics performance

Wiring is causing safety risks, fire and wire events in aircraft. Signal wiring usually makes up the bulk of aircraft wiring and is prone to wire events. Classifications of signal wiring by functional types are: Discrete DC low voltage; Instrumentation - Systems, analog; Synchro - 3-phase a.c.; Balanced systems (Differential); Signal lines (High Frequency Analog to Low Frequency); Full Digital Twisted Pair (Not Data Bus); Digital Data Bus; Safety Ground Wires. The circuit characteristics of signal wiring changes based upon a systems operational frequency. With increasing frequency, system circuit design and electrical stability becomes more critical. Variations in signal wire insulation electrical parameters are often the culprit where aircraft systems wire events are frequently experienced. Signal wiring insulation is extruded, wrapped or a combination of both, has a total thickness of approximately 0.004 of an inch and does not have a protective shield or moisture barrier. This leaves signal wiring open to various failure modes. The dominant failure modes are bending stresses, variations in temperature and hydrolytic scission. These failure modes require electronic tooling to identify and locate the insulation breaching whereas wire conductor failure is easier to locate and requiring less sophisticated tooling. Neither wire nor wire insulation failures are easy to locate visually, particularly when the wire migrates between locations within a given wire bundle on the aircraft. When failure occurs due to scission the equivalent circuit, as a result of the failure, takes on a new set of electrical parameters. The altered electrical parameters can cause failure of the entire electronic system by creating circuit instability. Additionally, the wire electrical and physical properties will never return to their original state after the initial failure. Wiring does not last the life of the aircraft. Recent events lead to the conclusion that wiring condition is safety related as indicated below: L1011 Honolulu to San Francisco arc fire in circuit breaker overhead. Crew controlled Fire and landed without loss of life; Indications are Swiss Air 111 and TWA 800 accidents may have been caused by electrical failure; San Jose, CA Airport experiences one emergency landing each week by commercial aircraft caused by smoke in the cockpit; Caledonia Airlines emergency landing with electrical fire