In repairs involving stringers on the lower surface of stressed skin metal wings, how are they viewed in terms of criticality?

Repairs involving stringers on the lower surface of stressed skin metal wings are viewed as more critical in reference to strength in tension due to the structural and aerodynamic loads that the lower surface endures during flight. The lower surface of a wing experiences significant tensile forces, especially in critical flight conditions, such as during takeoff, landing, and maneuvering. If a stringer, which provides support and contributes to the overall structural integrity of the wing, is compromised, it can lead to serious repercussions.

The distinction between the lower and upper surfaces is important because the lower surface typically bears more tensile load as the aircraft generates lift. This tensile load creates a greater demand on the structural members located there. As a result, repairs to lower surface stringers necessitate rigorous standards to ensure they can withstand these loads without failing. Therefore, ensuring that repairs are robust and effectively restore strength in tension is paramount, making these repairs more critical than those on the upper surface.