Originally Posted by
Feathers McGraw
Could the dirty lower nacelles be due to oil leaks, maybe over the whole flight? I know it's both engines but maybe there was some sort of systematic maintenance error.
If the oil loss is total then both engines could run down due to lack of lubrication.
Assuming the engine is a CFM 56 (a guess but maybe representative) there are U Tube videos showing how to rebuild the oil pump. Pump, manifolds and lines are mounted on the bottom of the fan ring...pretty much exactly where you see the black soot (maybe dirty oil?) trail start from in the pictures. If it touched the ground at all I would expect some of those lines got crunched.