A hat-stringer assembly for an aircraft, the hat-stringer assembly comprising: a hat-stringer, comprising: a first hat-stringer leg that comprises a first-hat-stringer-leg surface; a second hat-stringer leg that comprises a second-hat-stringer-leg surface, wherein the second hat-stringer leg is spaced apart from the first hat-stringer leg; a first hat-stringer sidewall, comprising a first-hat-stringer-sidewall surface, extending from the first-hat-stringer-leg surface; a connecting wall, extending from the first hat-stringer sidewall and having a virtual connecting-wall symmetry plane, passing through the connecting wall; a second hat-stringer sidewall, comprising a second-hat-stringer-sidewall surface, extending from the connecting wall to the second-hat-stringer-leg surface; and a ventilation opening, extending through the connecting wall; and a fitting, coupled to the hat stringer and comprising: a first channel member, comprising: a first-channel-member sidewall, in contact with the first hat-stringer sidewall; a first-channel-member base leg, extending from the first-channel-member sidewall and in contact with the first hat-stringer leg; and a first-channel-member cap leg, extending from the first-channel-member sidewall; a second channel member, comprising: a second-channel-member sidewall, in contact with the second hat-stringer sidewall; a second-channel-member base leg, extending from the second-channel-member sidewall and in contact with the second hat-stringer leg; and a second-channel-member cap leg, extending from the second-channel-member sidewall; and a web cap, in contact with the first-channel-member cap leg and the second-channel-member cap leg, wherein the web cap comprises a web-cap opening, which is in fluidic communication with the ventilation opening. a hat-stringer, comprising: a first hat-stringer leg that comprises a first-hat-stringer-leg surface; a second hat-stringer leg that comprises a second-hat-stringer-leg surface, wherein the second hat-stringer leg is spaced apart from the first hat-stringer leg; a first hat-stringer sidewall, comprising a first-hat-stringer-sidewall surface, extending from the first-hat-stringer-leg surface; a connecting wall, extending from the first hat-stringer sidewall and having a virtual connecting-wall symmetry plane, passing through the connecting wall; a second hat-stringer sidewall, comprising a second-hat-stringer-sidewall surface, extending from the connecting wall to the second-hat-stringer-leg surface; and a ventilation opening, extending through the connecting wall; and a first hat-stringer leg that comprises a first-hat-stringer-leg surface; a second hat-stringer leg that comprises a second-hat-stringer-leg surface, wherein the second hat-stringer leg is spaced apart from the first hat-stringer leg; a first hat-stringer sidewall, comprising a first-hat-stringer-sidewall surface, extending from the first-hat-stringer-leg surface; a connecting wall, extending from the first hat-stringer sidewall and having a virtual connecting-wall symmetry plane, passing through the connecting wall; a second hat-stringer sidewall, comprising a second-hat-stringer-sidewall surface, extending from the connecting wall to the second-hat-stringer-leg surface; and a ventilation opening, extending through the connecting wall; and a fitting, coupled to the hat stringer and comprising: a first channel member, comprising: a first-channel-member sidewall, in contact with the first hat-stringer sidewall; a first-channel-member base leg, extending from the first-channel-member sidewall and in contact with the first hat-stringer leg; and a first-channel-member cap leg, extending from the first-channel-member sidewall; a second channel member, comprising: a second-channel-member sidewall, in contact with the second hat-stringer sidewall; a second-channel-member base leg, extending from the second-channel-member sidewall and in contact with the second hat-stringer leg; and a second-channel-member cap leg, extending from the second-channel-member sidewall; and a first channel member, comprising: a first-channel-member sidewall, in contact with the first hat-stringer sidewall; a first-channel-member base leg, extending from the first-channel-member sidewall and in contact with the first hat-stringer leg; and a first-channel-member cap leg, extending from the first-channel-member sidewall; a first-channel-member sidewall, in contact with the first hat-stringer sidewall; a first-channel-member base leg, extending from the first-channel-member sidewall and in contact with the first hat-stringer leg; and a first-channel-member cap leg, extending from the first-channel-member sidewall; a second channel member, comprising: a second-channel-member sidewall, in contact with the second hat-stringer sidewall; a second-channel-member base leg, extending from the second-channel-member sidewall and in contact with the second hat-stringer leg; and a second-channel-member cap leg, extending from the second-channel-member sidewall; and a second-channel-member sidewall, in contact with the second hat-stringer sidewall; a second-channel-member base leg, extending from the second-channel-member sidewall and in contact with the second hat-stringer leg; and a second-channel-member cap leg, extending from the second-channel-member sidewall; and a web cap, in contact with the first-channel-member cap leg and the second-channel-member cap leg, wherein the web cap comprises a web-cap opening, which is in fluidic communication with the ventilation opening.