Jet fuel is stored in five locations in an F-16 including: (1) the wings, (2) a large fuel bladder located behind the cockpit, (3) gas tanks on the wings and/or center fuselage, (4) Conformal Fuel Tanks (CFT’s) and (5) the aft fuselage that surrounds the engine. The aft fuselage that surrounds the engine is also called the fuel cell area. The purpose of this blog is to: (a) describe the wiring harnesses in this area and (b) provide reasons why these wiring harnesses should periodically be inspected and possibly be replaced.
For about the first 2,000 F-16’s manufactured, the wiring harnesses in the fuel cell area were made with convoluted, protective tubing. Convoluted tubing was selected because these wiring harnesses were surrounded by jet fuel. Special transitions were designed to connect the interface from one leg of the wiring harness to another leg. Likewise, special backshells were designed to connect the convoluted tubing to the backshells and ultimately the connectors. Figure 1 below shows what one of these fuel cell wiring harnesses looks like. Notice the plastic-like tubing that covers the wires.
Figure 1 – F-16 Convoluted Tubing Wiring Harness
Normally, F-16 wiring harnesses have a Nomex braid that protects the wires underneath. Figure 2 below shows a typical F-16 wiring harness with Nomex braid. The engineers who first designed the F-16 did not want to submerge a Nomex braided wiring harness in jet fuel; therefore, instead, they designed convoluted tubing wiring harnesses.
Figure 2 – Nomex Braided F-16 Wiring Harness
The convoluted tubing wiring harness was a good design, but as stated earlier, after the first ~2,000 F-16s a design change was made. Instead of convoluted tubing wiring harnesses, the F-16 engineers changed the design to injection molded wiring harnesses. Later model F-16s, including the ones currently being manufactured, are all injection molded wiring harnesses for the fuel cell area.
Now you know what a fuel cell wiring harness is. The next question is “Why Replace Them?” The answer is the same for any component on the F-16. After many years’ worth of flying, all parts start to wear out and need to be replaced. The same is true for convoluted tubing wiring harnesses. Most of the aircraft that have convoluted tubing wiring harnesses are Block 15 F-16’s. Most of these jets are more than 25 years old. Just think about it; the convoluted tubing wiring harnesses in the fuel cell area have been sitting in jet fuel now for over 25 years! That a long time for anything to be sitting in jet fuel!
These wiring harnesses are difficult to access so most people who work on and maintain the F-16 do not get to see them. Additionally, there are many panels (that are sealed to make sure jet fuel does not leak) that have to be removed in order to inspect these wiring harnesses. It is not uncommon for these old wiring harnesses to have breaches in the convoluted tubing and thus the Kapton insulated wire underneath is now also soaking in jet fuel for many years! The only solution is to replace these old wiring harnesses with new ones. Thus, the reason to replace the fuel cell area wiring harnesses is because of: (1) age and (2) breaches in the convoluted tubing.
InterConnect has manufactured many replacement convoluted tubing wiring harnesses. If you want to purchase a ship set of them, please let us know. In case you are unfamiliar with the F-16 convoluted tubing fuel cell wiring harness part numbers, they range from H16DW701, H16DW702, H16DW703, and so forth to H16DW727.