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

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Multiple Choice

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

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.

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.

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