The watertightness and the problem of leaks is an issue of great importance in the general aviation sector and in particular for airlines, as it is one of the main causes of what is known as the Aircraft on Ground. In the case of fuel system or fuel tank leaks, the problem is little known to the general public, as it is something that does not usually come to light, unless the leak occurs in mid-flight, which would result in an emergency landing. It is precisely fuel leaks that have prompted civil aviation authorities to prescribe emergency procedures as part of the operating manuals, which are a requirement to be taken into account in order to maintain the airworthiness of aircraft. It should be borne in mind that the fuel tanks of modern aircraft are the wings, which are far from simple tanks. They are complex structures consisting of two shells joined together by ribs and stringers using thousands of rivets or bolts and where significant amounts of sealant are applied, precisely to try to ensure watertightness.
Technological innovation is key in the aeronautical sector, not only to improve aircraft efficiency, but also to ensure product quality.
But in an aircraft it is not only the fuel system that can leak. There are many aircraft systems that manage fluidsThe hydraulic system, which provides hydraulic power to the aircraft's flight control surfaces, landing gear, braking systems or doors, the pneumatic system or environmental control system, responsible for maintaining temperature and pressure in the various compartments of the aircraft, the oxygen system, the fire extinguishing system or the inertisation system also handle fluids in gaseous or liquid form.
After the occurrence of a leakage the next problem is its location. The complexity of aircraft systems sometimes makes this like looking for a needle in a haystack. It is therefore necessary to use the latest technology. Traditional methods of leak detection in the aviation industry are based on the measurement of pressure changein the use of soapy water to visually locate the leak by the generation of bubbles or in the use of UV-sensitive liquids which, once applied to the leakage area, change colour to show the location of the leakage. They are also used ultrasonic systems capable of detecting the leak from the sound produced by the fluid as it exits. In recent decades, newer techniques have been implemented in the aeronautical sector and have been used in other sectors such as nuclear energy, pharmaceuticals and the automotive industry. These methods are based on the use of a tracer gasusually very light gases such as helium or a mixture of nitrogen and hydrogen known as forming gas both of which are safe for humans and can be used in industrial environments. The method consists of introducing the tracer gas into the system and inspecting it with equipment known as a sniffer the area where the gas is believed to be leaking until the leakage of the gas in question is detected. In the sector oil & gas infrared cameras are used to detect leaks of gases such as butane or propane. This technology, based on electromagnetic absorption of gases in the infrared spectrum, is being technologically evaluated in aircraft systems using CO2 as a tracer gas.
Each of these methods offers a different sensitivity when detecting leaks. A system is considered to be watertight if it does not allow leakage of less than 10-2 mbar-L/s, compared to bacteria 10-4 mbar-L/s, the leak tightness requirements for fuel or gas systems are an order of magnitude higher, in the order of 10-5 o 10-6 mbar-L/s.
Technological innovation is key in the aeronautical sector not only to improve aircraft efficiency, but also to guarantee product quality through production processes and to comply with the required safety standards.
AERTEC Solutions participates as a core partner in the Clean Sky 2 programme within the consortium formed to implement the PASSARO project (caPAbilities for innovative Structural and functional teSting of AeROstructures). Within the framework of this project, AERTEC is leading a work package whose main objective is to contribute to the development of leak test benches that reduce process times and associated costs, and increase reliability levels when it comes to guaranteeing the leak tightness of aircraft systems that handle fluids.
The PASSARO project receives funding from the Clean Sky 2 Joint Programme under the European Union's Horizon 2020 Research and Innovation Programme under grant agreement No CS2-AIR-GAM-2014-2015-01.
