active noise protection

A stationary engine test (a so-called "run-up") is prescribed after aircraft overhaul and after work conducted on the engine-related aircraft systems as part of nightly maintenance operations. At the end of this, the functionality of all power units and the interaction of cockpit systems and engines is tested. Both the starting of the engines and the run-up for different power levels generate noise emissions in the surrounding area. In order to protect both staff on site and the residents of the areas around the site, Lufthansa Technik has used a noise protection hangar since 1961 as a form of active noise protection for engine run-ups. In 2002, the existing structure was no longer suitable for modern, wide-bodied aircraft, and it was replaced by the world's first enclosed noise protection hangar on Apron 6 at the Lufthansa base.  

The hangar is constructed with two doors at the front opening, at an angle of 45 degrees, and with rounded fins made of perforated plates of noise-absorbing material. The fin doors are repositioned so that the air intake flows free of turbulence in a laminar way into the hangar and through the engines, regardless of the wind direction. Additionally, noise dispersion towards the front is greatly reduced. Each of the two fin doors is 56 meters wide and weighs 300 tonnes. They are mounted on running gear and moved by electric motors. At the rear side of the hangar, exhaust emissions are deflected upwards by a sloped wall of perforated plates.  To avoid loud whistling noises, noise-reducing materials have been incorporated into the deflecting wall. The hangar is 95 by 84 meters with a height of 23 meters and can cater for aircraft up to the size of a Boeing 747-8.
The acoustic acceptance inspection measurements conducted in December 2001, involving a maximum load test Boeing 747-400 fitted with the most power motors available for the aircraft, already showed that the requirements are not only met, but that the noise emissions are in fact significantly lower than the official limits. The high availability of the hangar, however, does not mean that no run-ups are conducted in the open. The hangar cannot be used for run-ups, for example, if it is already in use or blocked for maintenance work, or if the tailwind speed exceeds eight knots.

January 2019