Which pattern indicates the engine was on the ground, based on soot patterns?

• A. Window pane: On the ground. Black soot all the way around; No aerodynamic flow pattern (Correct)
• B. In flight: Dark soot from origin, gradient aft in direction of the airflow
• C. Uniform soot around engine
• D. No soot deposition

Answer: (A)

When an engine is operating on the ground, the surrounding air is relatively still, so the exhaust soot isn’t blown in a particular direction. This produces a pattern with soot deposited all around the engine, showing no distinct aerodynamic flow direction. In contrast, in-flight operation puts the engine in a fast airstream, which carries soot downstream, creating a visible gradient or streaking from the origin in the direction of the airflow. A pattern with soot all around and no directional flow signal specifically points to ground operation, while patterns showing a directional trail or no soot deposition don’t fit a ground-start scenario.