Volume 31, Issue 3 (July 1986)
Lightning Damage of Bearing Surfaces in Turboprop Aircraft Engines
During the servicing of turboprop engines from aircraft which had reportedly sustained lightning strikes, the No. 5 main bearing from Pratt and Whitney, Type PT-6A engines, was often found to be pitted on its bearing surfaces to a degree that required replacement. This bearing is located deep inside the engine housing and is preceded by the No. 6 propeller shaft bearing at the front of the engine casing. Microscopic examination of the pits in the rolling contact surfaces of the examined No. 5 bearings appeared to show a wear pattern similar to that obtained on bearing surfaces by delamination during mechanical wear. When examined at high magnifications in the scanning electron microscope (SEM), it was found that the brightly reflecting bases of many of the pits had a dendritic structure and striations as a result of molten metal flow. Sectioned views through several pits confirmed that the metal base portions of these pits had indeed been remelted. The only energetics that could have accounted for this type of structure in pitted bearing surfaces was rapid melting and cooling by intense electric discharges through very small contact areas in mating bearing surfaces.