The negative pressure test process requires three specialists — one inside of the tank, another outside to run the pressure test equipment, and one safety attendant. They manage their safety procedures by following the guidelines, notes, warnings, and cautions listed in ATA Chapter 28 of the specific aircraft maintenance manual.
“Before entering the fuel tank our specialists use a gas detector to test the atmospheric conditions to ensure the tank is within the safety limits,” Rose says. They also use the required safety clothing, tools, and explosive-proof lights. Once the specialist is inside the fuel tank and in position, a vacuum is pulled on the tank. Rose recommends that “a good place to start troubleshooting is to look for previous repairs that have multiple layers of sealant.” In his experience, “integral wing tanks leak most often and common root causes are loose or deteriorating sealant, worn fasteners, and cracks in the wing structure and previous repairs.”
I asked Rose to tell me about their fuel tank maintenance specialists. What motivates them to work day in and out in a confined, explosive, toxic environment, chasing, and fixing problematic fuel leaks? “We usually recruit staff with former fuel tank maintenance experience. Some have A&P certificates, others don’t, but all attend in-house training programs. AOG has very low turnover and our specialists have the time and opportunities to develop their skills and personal expertise. In my opinion they are motivated to perform fuel tank maintenance because they are experts in their field. They have a lot of pride and respect for their team members because they do what others often cannot.”
Recently another group of leak-finding experts has given aircraft owners and operators and AMTs another product to help pinpoint aircraft fluid leaks. Spectronics Corporation has been a good friend to a variety of maintenance departments for a long time. It invented fluorescent leak detection and has provided us with ultraviolet dyes and inspection lamps for over a half a century. The 200-employee company headquartered in Westbury, NY, manufactures and distributes more than “1,000 different UV, UV/Blue and LED products that are used to find flaws and leaks in a multitude of mechanical systems.”
It produces the Aero-Brite universal fluorescent leak detection dye that can be used to locate leaks in all petroleum- and synthetic-based aviation fluid systems. Aero-Brite is “safe to use in aircraft fuel, hydraulic, and lubricating systems” and “safe to use in turbine and reciprocating engines.” Using the Aero-Brite for leak detection is about as easy as it gets. You add a prescribed amount of fluorescent dye to the leaking fluid system and let it circulate.
It can be used under all normal operating conditions and temperatures. When the mixture escapes at the leak site it glows a bright fluorescent yellow-green color when illuminated with a Spectroline high-intensity UV inspection lamp. The Aero-Brite comes in three different quantities and the OPX- 365 VV LED flashlight with a 20-foot inspection range can be used to check for leaks in those hard-to-get-to places.
According to Daniel Cooper, sales account manager at Spectronics Aviation Division, the MAXIMA aviation leak detection kit would be a better solution for specialty shops and crews needing a more robust system. Cooper suggests that “using the fluorescent leak detection products will help decrease the number of aircraft grounded for repair work.” As a tip to AMTs using Aero-Brite, the company recommends that “wherever possible, leak sites should be scanned with the UV lamp under low ambient light conditions in order to enhance the fluorescent response of the dye.”
Most AMTs that I have worked with have a personal zero-tolerance for leaks, drips, bubbles, streaks, and stains. Finding and fixing leaks calls for excellent systems and structural knowledge, safe tools and equipment, and time to do good detective work. Success usually comes to those AMTs that have patience and persevere. Often the only tactic that works is watchful waiting. Waiting until the loose B-nut, worn rivet, or pinched O-ring finally gives up its secret location. Good hunting. AMT