Correct me if Iīm wrong. This is a very normal thing to see, especially with cold engines (larger turbofans eng. such as the RB211 (older ones) PW4000, and on some JT9D) It is allso seen during shut down. On some engines it is fuel (from the nozzels or other areas) that is purged into the turbine to make a "controled" cooling/warm up during startup/shutdown. It can allso be oil from pressure bearings, where the internal pressure keep the oil on the "oil" side of the bearing, and when the engine is spooled up the oil press is greater that the press that keep the oil "inside" so to speak. And during spool down, the internal press is decreasing, and since oil press is greater some oil is let into the engine hot section and come out as smoke.
On other engines this allso happens, but at a much smaller scale and mostly not visible.
Is allso depends on what kind of ignitor plugs the engings have. The "glow" type will smoke more than the "spark" type, donīt ask me why, but thats what I been told.
[This message has been edited by Danish Pilot (edited 19 April 2001).]