The term 'Plane Designer's Concern' can be summarized as the need for efficient AIRFLOW. AIRFLOW is an important factor in aircraft design, as it affects the performance of the plane. The seven-letter solution to this term is 'AIRFLOW, ' which refers to the movement of air around the plane. AIRFLOW is necessary for the plane to generate lift and reduce drag, both of which are essential for a successful flight. Additionally, AIRFLOW helps to cool the engines and other components of the plane, ensuring that they remain safe and operational.