Quiet at last!

Noise attenuation in the hangar

When the maintenance work on an aircraft includes checking the avionics, a special on-board cooling system ensures that the equipment does not overheat during the layover in the hangar. But the cooling air that flows out of the air outlets of the aircraft generates a very high level of noise which constitutes a considerable noise nuisance to the mechanics in the vicinity, and in the long term it can even cause damage to health. It is therefore essential to have suitable health and safety and noise protection measures in place.

Lufthansa Technik has succeeded in reducing the noise caused by the escaping cooling air to a minimum with the aid of a noise attenuation system known as "Silencer", for which a patent application has been filed. The system is suitable for use on the Airbus A330, A340 and A380 and the Boeing 757, 767 and 777 widebody aircraft. The starting point for Silencer was a sound absorber developed for the Airbus A300-600, which was modified for the present purpose and adapted to fit the various widebody types.

Silencer consists of a cylindrical body that is lined with pyramid acoustic foam. Attached to the upper edge is a thick foam lip seal. The system is installed on a stand fitted with rollers, and vertical adjustment is supported by a pressurized shock absorber. Silencer is positioned under the aircraft air outlet. After the pressurized shock absorber has been released by pressing a button, Silencer slowly extends upwards and forms a seal with the aircraft outer skin.

The escaping cooling air is now conveyed through Silencer and the noise is absorbed in its acoustic lining. As a result, the noise level by the air outlet on the aircraft can be reduced from 105 dB(A) to 74 dB(A), and at a distance of three meters from 95.5 dB(A) to 68.8 dB(A).

In Franke Care System GmbH Lufthansa Technik has found a suitable partner to refine Silencer and series produce it. In this way the noise attenuation system will not just be used at Lufthansa Technik but may be purchased by interested aircraft manufacturers and MRO providers worldwide.