Finding and Fixing Fuel System Leaks

Finding and fixing leaks calls for excellent systems and good detective work.

Leaks, drips, seeps, bubbles, streaks, and stains make AMTs nervous. We all have read the allowable limits for these events and while that is good information, the truth is it usually doesn’t matter. These items are an affront to our quality code, our beliefs, and who we are.

To most AMTs a leaking, dripping, bubbling system or a stained and streaked fuselage, pylon, or cowling tells us that something is not quite right with our airplane. These things make us suspicious because we feel they could be indications of something coming that would be unpleasant, expensive, or affect normal aircraft operations or safety.

We worry about them, we think about them when we are away from the job, and sometimes we become obsessive. We check that B-nut one more time, wipe the bottom of that valve again, look on the ramp under the cowling again, or shine our flashlight on the bottom of the wing just to be sure. Often the drip will run and drop far from the source.

Fuel leaks

Finding and fixing aircraft fuel tank leaks has always been an arduous and time-consuming process, many times best left to a specialists. Generally, the aircraft is pulled from service and parked in a hangar or designated safe area. The general area of the leak is marked; the tank defueled, opened, vented, and allowed to dry. Next the AMT dresses in anti-static clothing, ensures that the tank environment meets safety standards, and enters the tank. The area in question is located, sealant removed, and fasteners replaced if necessary. The worked area is cleaned and prepped for the reseal. The sealant is allowed to dry and openings are closed. The tank is pressurized with shop air and the suspected area is sprayed with a soap solution. AMTs watch for telltale bubbles. If they do appear, the process is repeated and oversized fasteners are installed and or another round of sealant is applied. If no bubbles appear the tank is refueled and put on watch for leaks. If no leaks appear the aircraft can be returned to service. Fixing leaks is a big part of an AMT’s professional life. It is also big business.


In 1985 two Dallas, TX, aviation entrepreneurs founded Aircraft On Ground Inc. (AOG) and began servicing the business and corporate market. Recently AOG and North American Aircraft Services (NAAS), both FAA certificated repair stations offering specialized services, partnered in order to better serve their customers in the commercial, MRO, defense, and corporate markets.

Today their headquarters is in San Antonio and they have offices in 25 locations around the U.S., and in the U.K., Panama, Canada, and Spain. Their combined aircraft maintenance service offerings have expanded to include structural repairs and modifications, engineering, NDT, line and heavy maintenance, and training. NAAS and AOG have global repair teams that can be dispatched to all customer work locations. Aircraft fuel system maintenance is one of their core specialties. They are the experts in aircraft fuel system troubleshooting, fault isolation, and fuel tank repair. NAAS and AOG have a combined staff of more than 300 employees who are very passionate about finding and fixing fuel leaks.

Craig Rose, vice president of operations, has about 20 years with the AOG and provides some of his expertise on the subject. He explains why NAAS and AOG deserve their reputation. According to Rose, their fuel tank specialists are absolute experts at quickly finding the fuel leak path and pinpointing the exact location and root cause of the leak. When asked about their leak-finding process he said that it all begins with good analysis. “The specialists use our Work Order Management System that contains fleet trend modules, electronic wing maps, and repair histories,” he says. Next they conduct both positive and negative pressure test to find the leaks.

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