In which section of a stressed skin metal wing are repairs or splices involving stringers usually more critical?

The lower surface of a stressed skin metal wing is considered more critical for repairs or splices involving stringers due to the load distribution and stress concentration that occurs during flight. The lower surface typically experiences higher tensile and bending loads when the aircraft is in flight. This area is subject to substantial aerodynamic forces, especially during maneuvers and turbulence, which means that any repairs or splices in the stringers must ensure that the structural integrity is maintained.

In contrast, the other sections, such as the upper surface, leading edge, and tail section, may not experience the same levels of critical stress as the lower surface. While these areas do require careful attention and maintenance, the lower surface is where the risk of failure could significantly impact the overall performance and safety of the wing. Thus, when conducting repairs or splices in stringers, particular focus is placed on areas where the structural loads are highest, which in the case of most wings, is the lower surface.