Countries which have adopted the class rating system for small aircraft typically require additional training and license endorsement for complexity features such as conventional undercarriage (tailwheels), variable-pitch propellers, retractable undercarriage, etc.
In countries that have adopted the class rating system for small planes, pilots usually need to complete additional training and obtain a special endorsement for advanced characteristics like tailwheels, variable-pitch propellers, and retractable landing gear, which require more expertise.