What distance must be maintained around the tail area of a regional jet aircraft due to engine exhaust?

Maintaining a safe distance around the tail area of a regional jet aircraft is crucial primarily due to the risks associated with engine exhaust. The correct distance of 20 feet ensures that personnel and equipment are kept out of the path of hazardous jet blast and exhaust fumes, which can be dangerous due to their high temperature and velocity. This distance helps to mitigate the risk of injury from being caught in the jet wash, especially during engine startup, taxi, and takeoff phases, when the engines operate at higher thrust levels. Additionally, maintaining this safe distance protects ground equipment and other aircraft from potential damage caused by the powerful exhaust jet generated by the engines.

In contrast, the other distances are either inadequate or excessive compared to the recommended safety guidelines that have been established for ground operations around regional jets. These guidelines are based on industry standards and best practices for safety in aviation operations.