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Five Common Mistakes When Designing Aircraft Modification Kits


In the last 20 years InterConnect Wiring has assembled thousands of aircraft modification kits (AKA mod kits, loose wiring assemblies, or LWA’s) for a wide variety of OEM’s (Original Equipment Manufacturers).  During this time InterConnect has witnessed some repetitive problems associated with these kits.  Currently there is no aircraft modification kit standard throughout the industry thus the design can vary widely from company to company.  Until there is an industry standard, design engineers and aircraft kit manufactures should start collecting and sharing information to develop a list of best practices.  Provided below is the start of such a list – five common mistakes made when designing aircraft modification kits.

Mistake 1 – Listing of Kit Contents Part Numbers

Over the years, many military part numbers have been superseded by new part numbers.  This is also true for non-standard parts and commercial aerospace parts.  Since aircraft mods are typically done on older aircraft, most of the part numbers listed in tech manuals are the older superseded part numbers. Because of these older tech manuals, it is important that engineers list the superseded part number as well as the new part number in the kit contents list.  It also helps the technicians who install the kits if the National Stock Number (NSN) is listed with the part numbers (just in case the technician needs to order more spare parts).


Mistake 2 – Extra Floor Stock Parts

Many aircraft maintainers and technicians do not have extra floor stock of small, inexpensive parts.  For this reason, the kit contents designer should add a few extra parts just in case some of the parts get lost or the kit manufacturer miscounts the quantity.  As an example for military electrical kits the requirement for a kit may be MS27488-20-2 filler plugs, quantity 4, and M39029/4-110 contacts, quantity 3.  Instead of listing the actual quantity needed, the designer may want to list MS27488-20-2 filler plugs, quantity 6, and M39029/4-110 contacts, quantity 5.


No. Wire length Requirement        (Feet) Extra wire Length to Add (Feet) Length to List in Technical Document (Feet)
1 1 to 5 2 3 to 7
2 5 to 10 5 10 to 15
3 10 to 20 8 18 to 28
4 20 to 50 12 32 to 62
5 50 and Above 20 70 and Above
Mistake 3 – Wire Lengths

One of the most common mistakes when designing electrical aircraft modification kits is wire lengths.  This is especially true for older aircraft where there is no CAD, 3D drawing. There is nothing more frustrating to kit installers than to be running new wire for a mod and come up short.  Wire is relatively inexpensive so extra wire does not add much cost to the mod kit.  This table shows recommended extra lengths to add to each wire in a kit.

Mistake 4 – TCTO’s or MWO’s Not Provided to Suppliers

Many aircraft mod kit designers do not provide the kit manufacturers with a copy of the technical installation document.  For the Air Force this document is called a Technical Compliance Technical Order (TCTO) and for the Army it is called a Maintenance Work Order (MWO).  By failing to supply this document, the kit manufacturer is left out of the “big picture”.  They do not know how the kit contents will be listed including: the order of installation, the part numbers, the nomenclature of the parts, nor the quantity of each part number.  By not providing the technical document, the end result for the installer may be a kit that does not exactly match the technical installation document.  This may cause confusion and mistakes when installing the kit.


Mistake 5 – Tooling Requirements

The final mistake is tooling considerations.  Many designers fail to take into account the small disposable tools needed for aircraft mods.  This is especially true for contact insertion and extraction tools.  These tools are plastic and easily damaged.  Depending on the size of the kit and the number of contacts that a mod requires, many extra plastic insertion and extraction tools should be included in the kit’s contents.

InterConnect has come up with a list of best practices for labeling individual parts in each package and the kit contents as a whole.  To acquire this list, click the button below.

Our License

We are the sole licensee of Lockheed Martin for F-16 electrical products. Through this agreement, we have access to Lockheed Martin’s F-16 engineering data, tooling and configuration control information. We also have a Technical Services agreement with Sikorsky for all of their aircraft. This agreement allows us to obtain their engineering data needed to rewire helicopters that Sikorsky manufactures.



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