Aircraft Maintenance: Black lights aren’t just for parties

One of the areas we focused on was the evolution of the engine break-in process, where Continental is completing work on its new test cells that use regenerative dynamometer machines to capture the engine output of new engines, measuring performance while reclaiming the energy produced by the engine in the form of electricity that can offset the power used by other parts of the plant. It’s a fascinating process that combines green business practices with improved technology for evaluating engine performance at the completion of new engine builds and overhauls. Compared to the traditional method of using a test prop or “club” on the engine, Continental’s new facility is light-years ahead, capturing data that can be referred back to for the life of the engine and even enhance new product development.

As the technicians were explaining the break-in process to me, we focused on a step in the process that many aircraft owners routinely struggle with: checking engines for leaks. Few things can be as annoying as a leaky engine, and even very small leaks can make a big mess inside an engine cowling. Because of the nature of cooling airflow inside the cowling, it can be quite difficult to trace an oil leak to its source. For example, I’ve seen just a few drops of oil from a crankshaft seal make a mess of the bottom cowl while leaving almost no visible residue at the source of the leak.

I was particularly interested in how Continental inspects new and overhauled engines for leaks in the test cell. The answer it turns out, is simple: black lights. Aircraft oil is naturally fluorescent in long-wave ultraviolet light (UV-A), making even the smallest amount of oil easy to spot. The technician demonstrated the process to me on a new engine that was being tested in the cell prior to shipping to a customer. The engine completed the run-in process, the cooling shroud was raised, and the lights were lowered. I joined the technician as he used a handheld black light to inspect the engine from every angle and was struck by how effective the process was. Even the smallest fingerprints of engine oil lit up like a crime scene. The brand-new engine was pristine, with the exception of a couple of locations where test equipment was attached, including a plate that covered the prop governor pad, simulating a constant-speed propeller governor for testing. I checked all of the usual suspects where I see oil routinely on older engines: valve cover gaskets, gaskets, etc. They all looked great.

Chatting with the folks at Continental, they offered some tips for using this technique:

• Thoroughly clean the engine (follow the maintenance manual carefully, cover all inlets/outlets and use an approved cleaning solvent).
• Ensure that everything is dry and ready for flight.
• Fly the airplane briefly in the pattern.
• Open the cowl.
• Bring the aircraft into a darkened hangar.
• Use a handheld black light and inspect for the glow of leaks.

There are a variety of products on the market to help mechanics spot oil leaks, including additives and other products. However, it turns out that you don’t need anything more than a trip to your local home improvement store (or a few minutes of online shopping) to pick up the best tool for the job. One tip is to get a fairly powerful, battery-powered black light that’s still small enough to maneuver inside the engine cowl. For short money, you too can become a master oil sleuth. Then you can go on to step two: fixing the leak. Until next time…happy flying!