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Leaks in aircraft

Jorge Cordero

Jorge Cordero

AERTEC / Aerospace & Defence Systems


Tightness and the problem of leaks are a matter of great importance in the general aviation industry and for airlines in particular, as it is one of the main causes of what is known as aircraft on ground. The case of fuel tank or system leaks is a problem that is hardly known by the general public because it is rarely announced, unless the leak happens during a flight, which would lead to an emergency landing. Fuel leaks have led civil aviation authorities to laying down emergency procedures as an integral part of operating manuals, a requirement that is taken into consideration to maintain an aircraft’s airworthiness. It has to be taken into account that the fuel tanks of modern aeroplanes are located in the wings and that they are far from being simple tanks. They are complex structures comprised of two casings connected by ribs and stringers and use thousands of rivets or bolts where substantial amounts of sealant are applied in an effort to ensure tightness.

Innovation is a key factor in the aviation industry, not only to improve aircraft efficiency on a day-to-day basis, but also to maintain the strictest quality and safety standards.

Leaks, however, do not only affect the fuel system in aeroplanes. Many aircraft systems manage fluids, such as the hydraulic system, which provides hydraulic power to the aeroplane’s flight control surfaces; the landing gear; the brake systems; the doors; the pneumatic system; the environmental control system, which is responsible for maintaining the temperature and pressure of the aeroplane’s different compartments; the oxygen system; the fire extinction system; and the inertisation system, all of which also handle fluids in a gaseous or liquid state.

After a leak appears, the next problem is to locate it. The complexity of aircraft systems means that at times it is like looking for a needle in a haystack. This is why it is necessary to use cutting-edge technology. Traditional leak-detection methods in the aeronautical industry are based on measuring pressure changes, using soapy water to visually locate the leak through the creation of bubbles or using liquids that are sensitive to ultraviolet light which change colour to reveal the leak’s location once they are applied to the area of the leak. Ultrasound systems capable of detecting a leak from the sound it makes as it issues out are also used. Other more innovative techniques have been implemented in the aeronautical industry in recent decades. These have been used in other industries, like the nuclear power, pharmaceutical and automotive industries. These methods are based on the use of a tracer gas, usually very light gases like helium or a nitrogen and hydrogen blend known as forming gas, both of which are not harmful to humans and can be used in industrial environments. The method consists of injecting the tracer gas into the system and inspecting the area where the leak is thought to be with a device known as a sniffer until a leak of the gas in question is detected. Infrared cameras are used to detect leaks of gases like butane or propane in oil and gas industry. This technology is based on the electromagnetic absorption of gases in the infrared spectrum and is being assessed in aircraft systems from a technology standpoint by using CO2 as the tracer gas.

Each of these methods offers a different degree of sensitivity when it comes to detecting leaks. A system is considered watertight if it does not allow leaks of less than 10-2 mbar·L/s and 10-4 mbar·L/s for bacteria. The tightness requirements for fuel or gas systems are of a greater order of magnitude of around 10-5 or 10-6 mbar·L/s.

Innovation is a key factor in the aviation industry, not only to improve aircraft efficiency on a day-to-day basis, but also to maintain the strictest quality and safety standards.

Aertec Solutions is participating as a Core Partner in the Clean Sky 2 Programme within the consortium set up to implement the PASSARO (caPAbilities for innovative Structural and functional teSting of AeROstructures) project. Within the framework of this project, AERTEC is leading a piece of work whose main objective is to contribute to the development of test benches for leaks that reduce process times and associated costs, and increase levels of reliability, all aimed at ensuring the sealing of all aircraft systems that handle fluids.

The project PASSARO has received funding from the Clean Sky 2 Joint Undertaking under the European Union’s horizon 2020 research and innovation programme under grant agreement No CS2-AIR-GAM-2014-2015-01.






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