Rapid processing of landing gear bushings

Mobile system for the measurement of landing gear components

When a 100-ton passenger aircraft touches the ground on landing, the landing gears are subjected to enormous loads. As a result, the design has to take into account numerous factors, such as the total weight of the aircraft, the weight distribution and the need to reduce maintenance and repair costs to a minimum. This makes it resource- and cost-intensive to design the landing gear for a passenger aircraft. To satisfy the high safety standards and guarantee a long service life for these landing gear components, regular maintenance, repair and overhaul are necessary.

In the course of the various in-depth landing gear overhauls that are carried out over the years all the bushings in the landing gear components have to be replaced every ten years if not earlier. Over the years corrosion can build up in the drilled holes and on the lateral surfaces of the bushings and components made of bronze, aluminum or steel. Whereas the bushings can no longer be used, the corrosion on the components can be removed by milling. However, the wall thickness and drilled hole diameters are different on every component, so that a new bushing that fits exactly has to be individually fabricated for each drilled hole. And after replacement, the component including the new bushings has to match precisely the dimensions prescribed by the original equipment manufacturer (OEM).

In the past both the measurement methodology and the manual calculation of the bushing dimensions used to take up a lot of time and accordingly were highly labor-intensive in terms of technical and administrative effort. After milling the components were first measured to an accuracy of a hundredth of a millimeter with hand-held instruments (caliper gauges, measurement guns, micrometer calipers and three point internal micrometers). The data was then noted down by hand and then entered into the SAP system. The new bushing dimensions (length, flange thickness and diameter) were then calculated from the resulting measurement data. The new dimensions and all the corresponding order information (order and bushing job number and person responsible) had to then be manually transcribed to the bushing drawings before being passed on to the colleagues in the machine group, who would then manually enter them into the CNC machine tool.

Working with the Department of Informatics of Hamburg University and Lufthansa Systems, Lufthansa Technik has developed a software that significantly simplifies the measurement process. It enables the bushing dimensions to be calculated automatically and the automatic transfer to the relevant technical drawings. By using a semi-automatic measuring arm, a lot of time can be saved, component measurement can be significantly improved and the error rate further reduced. The measuring arm automatically transfers the component dimensions thus ascertained to the SAP system. The SAP system calculates all the necessary dimensions of the new bushings and controls the printing of all necessary order documents and drawings. As a result, the effort required to manually transfer the data and perform the associated administrative tasks is drastically reduced. Only the entry of data for the new bushing dimensions into the CNC machine is still performed manually, but in the future this too will be automated.

With the results of the research project it has been possible to successfully combine the work steps "component measurement", "calculation of bushing dimensions" and "bushing production", which were previously largely independent, into a coherent, integrated system. As a result only a few, optimally interconnected interfaces are now required. Linking all the measurement methods and automating the work processes has not only made it possible to reduce process times by up to 30 percent, but the already high quality standards have been improved still further. To ensure that the findings can be used by all of the network partners in the future an intensive information exchange has taken place with all the subsidiaries and affiliates of the Lufthansa Technik Group that are involved in landing gear overhauls. A patent application for a "mobile measurement system" that incorporates the results of the "Software Development Bushings" research project, which was funded by the Federal Ministry of Education and Research, has already been filed.