Engine maintenance and repair is a large part of the total airplane operating cost. Routine maintenance is essential for providing a positive impact on lifetime, engine performance and reliability. The sector of on-wing and near-wing maintenance is growing because of its potential to reduce the expenses and inspection time, with diagnostics taking place close to the airplane or inside a hangar on the airport. Due to the high complexity of modern jet engines, this task creates special needs towards the measurement systems regarding flexibility and robustness.
This paper describes four design approaches of such measurement systems to determine the engine parts’ health status with complex geometries in narrow or occluded spaces between blades and individual discs. The utilized nondestructive technologies are endoscopic fringe projection for geometry measurement, adapted low coherence interferometry to determine surface microstructures, high frequency inductive thermography with an optical mirror and miniaturized high frequency eddy current testing for inspection of the protection coating system and for the detection of subsurface cracks and defects. The inspection information obtained by all these techniques can be further used for regeneration process simulations and functional simulations to predict the optimal overhaul strategy.