XL-ETFE insulated wires can be found on many commercial and military aircraft built since the 1980s and need to be included in the study of XL-ETFE aircraft wire degradation. As such, some aircraft have been operating for 30 years with the same wiring. The question that becomes more important with each passing day is the wire degradation of the insulation and its impact on the aircraft airworthiness.
There are ways to identify some signs of XL-ETFE insulation degradation. As the wires are exposed to elevated temperatures, the insulation discolors to a brown hue. An example of this can be seen in the photo below. These wires were exposed to an elevated temperature for a brief duration (less than 2 hours @ 260oC) before reaching this color.
With continued exposure to elevated temperatures, the XL-ETFE insulation becomes a darker brown. It is important to note that the color will vary dependent on the particular insulation formulation (the particular formulation varies between manufacturers).
Alone, wire insulation visual examination is not enough. There is a need to identify the wire insulation quality and for how much longer the wire can be considered reliable. To this end, Lectromec has been investigating the degradation mechanisms of XL-ETFE insulated wires. Designed as a three phase effort, phases I and II examined different mechanisms for the XL-ETFE performance degradation and methods to quantify the impact on system reliability. Phase II of the research has been completed and has yielded very exciting, consistent test results.
On May 30th, 2011, Lectromec announced that it was entering the third phase of the research effort. Phase III of the research is set to investigate the practical limitations of aged XL-ETFE. This will examine the level of mechanical stress that can be endured before insulation system failure (stresses akin to standard maintenance actions on an aircraft). This research will include the development of the data sets necessary for the comprehensive XL-ETFE degradation life projection model.
If you are interested in aerospace wire degradation, you may want to read the Wire Degradation and Looking in the Arc article.
The XL-ETFE degradation research will nicely supplement Lectromec’s growing body of wire insulation degradation analysis technologies that are a key part of Lectromec’s Electrical Wire Interconnection System (EWIS) risk assessment technologies for existing fleet life extension programs.