Why not perform certification test on aging wire?

Author: Lectromec - Michael Traskos
Published: 03-22-2012

Before a wire is first brought onto an aircraft, it must first go through a series of tests that validate the quality of the finished wire. Most of these tests are conducted on new wire not subjected to accelerated aging. Because of this, the question will arise asking if testing an aged wire (one that has been on an aircraft for a number of years) to the original new wires tests would give a good picture of the wire condition.

First, it is important to consider what should be determined from the testing of an aged wire. Ideally, the testing should determine the following:

1. What is the current condition of the wire?
2. Can the wire remain on the aircraft?
3. If the wire can remain on the aircraft, how much longer should it stay on the aircraft?
4. Should the wire be removed now?

These questions are at the heart of any aircraft (or any vehicle) life extension effort. Aside from answer question #1, would selective sampling and testing of wire from the aircraft to new wire specifications answer any of these?

Directly, the answer is ‘no’, but it would certainly provide data to help make decisions. Some engineering decisions are needed at the initiation of such a project because the specification testing can take months to complete. The questions that immediately come to mind when considering this path include:

1. Should all the tests be performed, or will only a subset be tested?
2. What if the wire does not pass one spec test? Does that mean the wire is not good enough to be on the aircraft?
3. If the wire does not pass one or more spec tests and it will be considered to remain on the aircraft, how much below the spec baseline will be acceptable?
4. Are there any existing guidelines to determine how much longer the new or questionable wires should remain on the aircraft?

These are not simple questions to answer. Ideally, this would be an excellent way to evaluate a wire if there was a defined degradation age data for each test spec. At this time, the level effort necessary to generate sufficient data is beyond the capabilities of most organizations. Additionally, there would need to be data from multiple manufacturers to make the model applicable where used.

From a practical and engineering perspective of focusing on simplified quantifiable values representing wire degradation, Lectromec recommended the use of wire degradation analysis technologies. These technologies are designed to examine a common physical wire insulation property that has been thoroughly tested under multiple conditions and analyzed as part of a complete dataset. From this research, wire life degradation models are developed directly applicable to most commonly found environments.

To find out more about these technologies and how they can be applied to your program, contact Lectromec.