A common question that military users and maintainers of aged aircraft ask is “when should their aircraft be rewired”? This is a very good question. Is it based on the number of flight hours or is it the number of years since it left the production line? Actually, there are additional and more important factors when making this decision. Here are the 5 Main Factors to consider when deciding to rewire a military aircraft. They are listed in the order of importance.
The Type of Insulation of the Wire
Surprisingly, the most important factor is the type of insulation of the wire in the aircraft. A wire that undergoes hydrolysis is more likely to become aged and brittle. Unfortunately, many of the more older aircraft have polyimide insulation. Polyimide insulation is the more technical name. A commonly known type of polyimide insulation is Kapton ™.
Environment Where it Was Operated
The environment is the second most important aspect when considering to rewire or not. An aircraft that is primarily operated in a wet, salty, and/or humid environment is more likely to need to be rewired much sooner than one that is operated in hot dry environment.
The Age of the Aircraft
The third main factor is finally the age of the aircraft. The age is defined as the number of years since the aircraft has left the production line. Generally speaking (and depending on the type of insulation and the environment where it was operated) rewire should start being considered once it is 20 years old. After 20 years, the cost benefit analysis starts to show it is more beneficial to rewire a fleet of aircraft than to keep maintaining and fixing wire related problems.
Number of Intermittent Problems Experienced Over the Past Year
The fourth item to consider is the number of intermittent and wire related problems that an aircraft experiences. Some aircraft seem to have more wire related problems than others. Typically, they either have a gremlin in them or were operated in a harsher environment than the other aircraft in the fleet. It is recommended that all intermittent problems be recorded and analyzed on a yearly basis. If this analysis is done over many years, trends will be apparent and help justify a complete or partial rewire of aircraft.
The Number of Flight Hours
Finally, the last factor is the number of flight hours. Many people think the number of flight hours is the most important factor when in fact it is not. The other four factors above have more of an effect on deciding when to rewire than flight hours. Flight hours however is a factor and should be considered. An aircraft flown more than other aircraft tend to have more intermittent and wire related problems than other aircraft.
InterConnect Wiring has done multiple studies analyzing older aircraft’s wire. Click below to get a copy of the first study that InterConnect performed.